a Statewide Approach to Adolescent Use Prevention’
DAVID M. MURRAY, PH.D., *,’ CHERYL L. PERRY, PH.D.,* GRETCHEN GRIFFIN, M.P.H.,? KATHLEEN C. HARTY, M.ED.,S DAVID R. JACOBS, JR., PH.D.,* LINDA SCHMID, M.A. ,* KATHY DALY, PH.D.,S AND UNTO PALLONEN, PH.D.§ *Division Minnesota Minneapolis,
of Epidemiology, School of Public Health, University of Minnesota, Minneapolis, 55454; tMinnesota Department of Education and iMinnesota Department of Health, Minnesota 55415: and §CJniversity of Rhode Island, Kingston, Rhode Island 02881
Background. The 1985 Minnesota Legislature established guidelines for school-based tobacco-use prevention programming and provided financial incentives to school districts to encourage them to adopt a broad range of preventive measures. The Minnesota-Wisconsin Adolescent Tobacco-Use Research Project was funded by the National Cancer Institute in 1986 to evaluate the Minnesota initiative through two parallel studies. Methods. The Four Group Comparison Study was a prospective study of 48 school “units” which were randomly assigned to one of four conditions in 1987. Baseline observations were taken in the sixth grade in 1987, interventions were delivered in the seventh grade, and follow-up observations were taken in the seventh, eighth, and ninth grades. The Four Group Comparison Study was designed to evaluate the three middle-school interventions that were most widely adopted by Minnesota school districts as a result of the 1985 legislation. The Two State Comparison Study was a serial cross-sectional study of representative districts in Minnesota and Wisconsin. Annual surveys of ninth graders were conducted from 19861990. The Two State Comparison Study was designed to determine whether tobacco-use patterns changed in Minnesota relative to Wisconsin following the Minnesota legislation. Results. The prospective study indicated that none of the interventions was more effective in reducing adolescent tobacco use compared with a randomized control group. The serial cross-sectional study revealed that there was a modest net decline in Minnesota relative to Wisconsin from 1986 to 1990, but that it was within the range of chance variation. Conclusions. Taken together, these results indicate that this legislative initiative was insufficient to reduce adolescent tobacco use statewide during the S-year study period. Together with results from other recent studies, they suggest that even more intensive efforts may be required to effect widespread reductions in adolescent tobacco use. 0 1992 Academic
In 1990, the National Cancer Institute (NCI) published guidelines for effective school-based tobacco-use prevention programs (1). These guidelines call for programs that focus on the social influences that encourage adolescents to smoke, provide training and rehearsal for skills to resist those influences, and correct student perceptions about social norms for smoking. Numerous studies published ’ This work was supported by a grant from the National Cancer Institute (ROl-CA-43323). ’ To whom reprint requests should be addressed at Division of Epidemiology, School of Public Health, University of Minnesota, 1300 South Second St., Suite 300, Minneapolis, MN 55454. 449 0091-7435/92
Copyright 0 1992 by Academic Press, Inc. All rights of reproduction in any form resewed.
over the last 15 years suggest that a curriculum based on this social influences model can reduce the onset of smoking among adolescents by 40-75% for at least 2 years (2-4). More recent studies suggest that such programs, delivered in early adolescence, may delay onset for many students for as long as 4 years (5-7). Some of our most recent work suggests that the effects may last even longer if these programs are delivered in the context of community-wide health promotion activities (8). In spite of this evidence, school districts have been slow to adopt curricula based on the social influences model (9). Administrators and teachers may not be aware of this research, may see other issues as having higher priority than tobacco-use prevention, or may not have adequate support for the teacher training and materials acquisition that would be required to implement new programs. The dissemination problem has been so common that the NC1 has funded two studies designed to develop and evaluate methods to disseminate effective smoking prevention programming across large geographic regions (IO, 11). More recently, the NC1 announced the ASSIST program which is designed in part to provide funds to states to encourage them to adopt such programs. In 1985, the Minnesota State Legislature passed a bill to encourage dissemination of effective tobacco-use prevention programs. The legislation provided approximately 50$ per pupil to districts that adopted programs which included the following components: (a) in-service training for teachers and staff; (b) evaluation of programs and curriculum results; (c) a K-12 continuum of interventions related to tobacco; (d) targeted interventions for students age 12-14 based on evaluated curricula; and (e) prohibition of tobacco use by minors on school property. The Legislature also provided funding to the Department of Education to administer the school-based effort, to guide the schools in the selection of appropriate programming, and to develop smoke-free policies. Funding was provided to the Department of Health to provide assistance to worksites to develop smoke-free policies, to provide technical assistance to local health departments, to conduct a long-term public information campaign to discourage tobacco use, to award local grants for innovative prevention and cessation efforts, and to conduct surveys to evaluate the impact of the legislation. Total funding per year was approximately $2 million, beginning in 1986. This effort represented the first such public policy initiative aimed at discouraging tobacco use across an entire state. The Minnesota-Wisconsin Adolescent Tobacco-Use Research Project was funded by the NC1 in 1986 to evaluate the impact of the Minnesota Legislature’s initiative on adolescent tobacco use (9). The project supported two complementary studies. The Two State Comparison Study compared the prevalence of adolescent tobacco use in Minnesota and Wisconsin based on annual cross-sectional surveys in the two states. It assessed the degree to which there was any measurable net decline in adolescent tobacco use in Minnesota relative to Wisconsin after 3 years of intervention in Minnesota. The Four Group Comparison Study compared the incidence and prevalence of adolescent tobacco use in schools randomized to the three middle school interventions that were most widely adopted as a result of the legislation or to an existing curriculum control group. It assessed the
degree to which any effect in Minnesota was largely due to the school component of Minnesota’s statewide intervention program. This article presents the main results from these two studies. Their results are combined because neither study alone adequately addresses the major research question, whether the 1985 Minnesota legislation had a beneficial effect on tobacco use among Minnesota adolescents. The Two State Comparison Study, by virtue of its nonrandomized design, inherently poses a number of threats to internal validity that make it difficult to interpret in isolation. The Four Group Comparison Study, by virtue of its randomized design, avoided most of those threats, but did not include a reference group outside Minnesota. To the extent that their results are consistent, the studies are most easily interpreted as a pair. TWO STATE COMPARISON
The Two State Comparison Study employed a nested cross-sectional design (12). Annually from 1986 through 1990,43-46 sampling units, defined below, were selected at random to represent each state. Ninth graders in those units were surveyed for tobacco use, exposure to traditional and social influences educational activities, and related variables. Approximately 3,600 students were surveyed in each state each year. Hypotheses
Minnesota ninth graders observed in 1986 and 1987 completed the seventh grade in 1984 and 1985, respectively, and so passed through the primary intervention grade prior to the implementation of programs sponsored by the Minnesota legislation. Minnesota ninth graders observed in 1988-1990 completed the seventh grade in 1986-1988, respectively, and so passed through the primary intervention grade after the implementation of programs sponsored by the Minnesota legislation had begun. There was no organized change in the level or type of tobacco-use educational activity in Wisconsin during the 19861990 study period. As a result, we hypothesized that (a) the 1986-1987 data from Minnesota and Wisconsin would present parallel trends on all measures, (b) the 1988-1990 data would present a net increase in Minnesota for exposure to social influences tobacco-use educational activity, and (c) the 1988-1990 data would present a net decrease in Minnesota for tobacco use prevalence. We expected stable agegender distributions in the two states over the 5-year study and included these measures primarily to allow indirect standardization of the dependent variables for these important covariates. Similarly, we had no a priori hypotheses concerning the reported smoking patterns of parents, friends, and peers, and included these measures in the study to facilitate interpretation of the results obtained for the dependent variables.
We expected equal weekly smoking prevalence rates of 15% in the two states at baseline. Since prior studies had reported reductions in new onset of Xl-75% over 2 years, we hypothesized that under more real-world conditions, we might see a net reduction in prevalence of one-third at the end of 5 years: to 10% in Minnesota if Wisconsin remained at 15% (9). Given estimates for the within-school dependence in the data due to cluster sampling (intraclass correlation coefficient of 0.02) and the variance reduction due to covariance adjustments (lo%), two-tailed tests, and a Type I error rate of 5% and power of 80%, we estimated that usable data would be required from 75 students from each of 44 sampling units each year in each state in order to detect a difference of this size (9, 12). Sampling Scheme
One of the goals in the Two State Comparison Study was to employ samples that represented the entire ninth grade enrollments in Minnesota and Wisconsin. As a result, we developed a sampling plan that gave each ninth grade student in those states a roughly equal chance of selection. Instead of sampling schools per se, since they vary widely in size, we defined a range for the size of an artificial sampling unit such that: (a) the largest unit would be no more than twice the size of the smallest unit and (b) the average expected unit size would be 14% larger than the required unit size obtained from the power analysis. A twofold range in the size of the sampling units is slight enough to avoid the need to weight the data in subsequent analyses (13) and gave us considerably greater flexibility in defining the units than we would have had with units of equal size. The 14% margin was added to allow for absent students, incomplete data, deviations in observed school enrollments from the estimates used in drawing the sample, and refusals. This approach called for sampling units ranging from 53 and 106 students each with an average expected size of 86. To create these sampling units, we gathered enrollment information for the ninth grade from each public school in both states in 1986.3 Schools with enrollments greater than the desired range were artificially divided into the smallest number of units possible such that all units from a given school were equal in size and fell within the desired range. Schools with enrollments smaller than the desired range were grouped at random with one or more other small schools until a unit was formed that fell within the desired range.4 Schools with enrollments that fell within the desired range were left intact. From the 468 Minnesota and 441 Wisconsin public schools that included ninth graders in 1985-1986,694 Minnesota and 781 Wisconsin sampling units were created. These units were listed in random order for each state and invited in sequence to participate in the Two State Comparison Study. When a unit declined participation, the next unit on the list for 3 Private school enrollment in 1986 was less than 10% at the secondary level. While exclusion of private schools from the study may limit the generalizability of the TSTP findings somewhat, the effect is modest at best and does not affect the internal validity of the study. 4 Schools with enrollments below 20 were excluded. They accounted for less than 1% of the total enrollment in the ninth grade in either state.
the same state was invited. This sampling unit construction dure was repeated independently for each year’s survey.
and selection proce-
The superintendents for each year’s selected districts were contacted by mail. The letter outlined the project and invited the district to participate; it was signed by the Commissioners of the Minnesota Departments of Health and Education and by the Principal Investigator (D.M.). Project staff followed up within a week by telephone to provide additional information, answer questions, and seek a commitment to participate in that year’s survey. Meetings with school districts were held as needed, with only one or two required per year. Survey
The procedures, materials, and staff were identical for all surveys in Minnesota and Wisconsin. Scheduling. Survey dates were established by the survey coordinator in consultation with the building principals. To minimize staff travel, schools in the same geographic area were scheduled during the same week whenever possible. The building principal selected a course which was required of all ninth graders, but not academically tracked; a number of classes sufficient to provide the necessary number of students was selected from those available for that course, and the ninth graders enrolled in those classes constituted the population eligible for the survey. All surveys were conducted in October and November, with survey activity progressing at the same rate and over the same calendar period in both states. Consent mailing. A consent letter was sent to the parent(s) of each potential survey participant approximately 2 weeks prior to the survey. The letter described the purpose of the survey and the methods to be used, and asked parents who had questions or did not want their child to participate to contact the project’s survey coordinator or their student’s building principal. This passive consent procedure was approved by the University’s Committee on the Use of Human Subjects and has now been used in similar studies involving over 150,000 observations in Minnesota and neighboring states. Survey procedures. On the date selected for the survey, project staff traveled to each participating school, where two staff members organized the survey operations in each classroom assigned for that purpose. Though teachers were asked to remain in the classroom, only the survey staff participated in the collection of data. Students whose parents refused (~0.1%) were excluded from the survey. After giving informed consent, participating students completed an anonymous questionnaire and provided an expired air sample for carbon monoxide analysis. Carbon monoxide in expired air is highly correlated (r > 0.90) with carbon monoxide in blood (14) and is moderately correlated (r > 0.65) with the number of cigarettes consumed in the last week among ninth graders (15). The carbon monoxide testing was done in the context of the “pipeline” procedure shown to enhance the disclosure of tobacco use by adolescents under similar survey conditions (16). Students were not informed of the results of their CO test to avoid
any effect on their survey (17). A more detailed description of these survey methods has been published previously (15). Quality control. All survey staff attended a training workshop held each year in March, where the survey coordinator and PI reviewed the procedures and materials. Senior staff, who had prior experience in similar school-based tobacco-use surveys, served as team leaders in each two-person team. Carbon monoxide testing equipment was calibrated daily. The survey coordinator observed each survey team in the field and gave additional instruction as needed. Variables of interest and their measures. The questionnaire assessed subjects’ demographics, cigarette smoking and smokeless tobacco use, perceived tobacco use by models, exposure in school to educational programs related to tobacco use, and other factors believed to be related to tobacco use. Cigarette smoking was analyzed using a composite smoking index, scaled to reflect the number of cigarettes per week (15). Smokeless tobacco use was analyzed using two items reflecting any use in the student’s lifetime or in the previous 7 days. Perceptions of smoking by models were assessed in a series of questions asking whether the student’s father, mother, older siblings, best friend, peer group, or other students in the same grade smoked or used smokeless tobacco. Exposure to traditional educational activities was assessed by asking whether the student had participated, since the beginning of the seventh grade, in a series of activities related to long-term health consequences, short-term physiological effects, tobacco use and pregnancy, or tobacco use as a habit. Positive responses in each category were summed, providing scores ranging from 0 to 4. Exposure to social influences educational activities was measured in a similar fashion, by inquiring about participation in social influences discussions, social influences activities, and peerled social influences activities. The Cronbach (Y coefficients for these exposure measures exceeded in 0.70 in grade 9. Analysis
The Two State Comparison Study design differed from the usual experiment in that the sampling unit was the unit of assignment, based on geography, while the individual student was the unit of observation. Students were selected for the surveys from within clusters defined by their sampling unit, which closely approximated their school. Based on well-known sampling theory, persons within a cluster tend to be more like one another than they are like persons in other clusters (13). This association, indexed by the intraclass correlation coefficient, adds an additional component to the variability of treatment group means above and beyond that attributable either to the individual subjects or to the treatments themselves (19). Unless this component is accounted for in the analysis, the evaluation of the treatment effects will be positively and often substantially biased m-0.
We accounted for the extra variation due to cluster sampling in the Two State Comparison Study through a hierarchical ANCOVA. State was crossed with year, while units were nested within the state by year surveys and students were nested within units. Students and units were treated as random effects while state and year were treated as fixed effects. The comparisons of interest were made by
comparing the mean square for the state by year interaction against the mean square for unit within state by year. Age and gender were included as covariates in all analyses. Results Participation
Table 1 summarizes the participation by schools and by students in each of the annual surveys. Participation by schools was generally higher in Minnesota than Wisconsin. Participation by eligible students was high and quite similar across both states and years. Demographics
Table 2 presents the state by year means for the demographic and smoking model variables; the smoking model means were adjusted for age and gender. Only two significant interactions were observed in these analyses: students in Minnesota reported a net decline in father’s smoking over time relative to students in Wisconsin (F = 2.41; df = 4,438; P = 0.0483), and Minnesota students were slightly older than Wisconsin students in 1986, though the difference disappeared by 1990 (F = 4.11; df = 4,438; P = 0.003). There were main effect differences between the states for several variables: Minnesota students reported lower rates of smoking by mothers (29.1% vs 31.9%; F = 12.49; df = 1,438; P = O.OOOS), older siblings (21.8% vs 24.8%; F = 27.32; df = 1,438; P = O.OOOl), best friends (23.7% vs 27.8%; F = 19.29; df = 1,438; P = O.OOOl), any friends (66.2% vs 71.0%; F = 13.15; df = 1,438; P = 0.0003), and age mates at school (70.4% vs
84.2%; F = 50.28; df = 1,438; P = 0.0001). The gender distribution was similar across states and years. These data indicate that the Minnesota students enjoyed with significantly fewer smoking models than their counterparts in Wisconsin and that this environment did not change appreciably over the 5 years of the study. an environment
Table 3 presents the state by year means, adjusted for age and gender, for the four variables that assessed exposure to traditional educational activities. Tradi-
TABLE AND STUDENTPARTICIPATIONINTHE
Schools Schools School rate Students Students Student rate
selected participating participation
87.8 eligible participating participation
3,871 3,580 92.5
91.9 4,252 3,936 92.6
91.3 4,000 3,772 94.3
86.2 3,969 3,615 91.1
89.4 4,230 3,926 92.8
87.8 3,838 3,576 93.2
85.7 4,184 3,958 94.6
85.7 3,758 3,456 92.0
95.2 3,779 3,457 91.5
81.4 3,484 3,190 91.6
TABLE 2 FORVARIABLESRELATEDTOCIGARETTE COMPARISON STUDY
Gender (% male) Age (years) Perceived smoking rates among models, adjusted for age and gender (%) Father Mother Other siblings Best friend Any friends Age mates at school
35.5 33.0 23.6 23.8 64.9 70.8
34.1 29.8 22.4 23.5 65.2 67.3
31.7 27.3 21.4 22.2 62.4 68.5
32.0 28.0 22.2 26.4 70.0 73.6
31.2 27.2 19.7 22.3 68.7 71.6
33.5 31.7 24.7 28.5 69.6 81.7
35.1 32.1 26.6 27.6 70.0 82.8
35.7 31.9 24.4 27.8 71.6 83.8
35.3 31.9 24.1 27.7 70.8 90.7
35.6 31.2 24.4 27.5 72.9 82.1
tional educational activities were not part of the statewide intervention effort sponsored by the Minnesota legislation, and we did not expect to find any state by year interactions for these variables. This expectation was supported by the data as there were no significant state by year interactions. There were main effect differences between the two states on all four variables, with higher exposure in Minnesota in each case: Long-term health (2.62 vs 2.38; F = 24.70; & = 1,438; P = O.OOOl), short-term health (2.26 vs 1.95; F = 37.98; u!! = 1,438; P = O.OOOl), smoking during pregnancy (2.16 vs 1.98; F = 13.02; df = 1,438; P = 0.0003), and smoking as a habit (2.30 vs 2.08; F = 24.53; & = 1,438; P = 0.0001). In addition, there was a significant though parallel increase over time for discussions about short-term health (F = 4.86; df = 4,438; P = 0.0008) and smoking as a habit (F = 4.34; df = 4,438; P = 0.0019). Figure 1 includes a graphic representation of the long-term health variable as representative of the measures of exposure to traditional educational activities (Panel 1). TABLE 3 ADJUSTEDSTATE BY YEARMEANS FORDEPENDENTVARIABLESRELATEDTOSMOKING Two STATECOMPARISON STUDY Minnesota
Self-reported exposure to traditional content (O-4) Long-term health Short-term health Pregnancy Smoking as a habit Self-reported exposure to social influences content Discussions Activities Peer-led activities Self-reported weekly smoking (%) Prevalence
2.53 2.02 2.05 2.15
2.47 2.09 2.04 2.13
2.74 2.43 2.25 2.48
2.67 2.34 2.23 2.38
2.69 2.41 2.27 2.38
2.38 1.91 1.95 2.03
2.35 1.90 1.93 2.03
2.42 1.93 1.96 2.11
2.33 1.93 1.97 2.04
2.44 2.10 2.09 2.19
2.21 0.64 0.36
2.15 0.71 0.43
2.49 1.28 0.77
2.28 1.01 0.64
2.48 1.13 0.66
2.03 0.61 0.35
1.95 0.57 0.35
2.05 0.66 0.38
1.93 0.79 0.47
2.08 0.83 0.53
Panel 1: Term Health
Panel 4: Term Health
Panel 5: Influences
Panel 3: Social Influences
Panel 6: Social Influences
B i Seventh
FIG. 1. Educational exposure outcomes.
These data suggest that exposure to traditional tobacco-use educational activities was higher each year in Minnesota than in Wisconsin and that the difference in exposure did not change over the 5 years of the study. Exposure
to Social Influences
Table 3 also presents the state by year means, adjusted for age and gender, for each of the three variables that assessed exposure to educational activities based on the social influences model. We planned to use these variables to assess the extent to which Wisconsin students were exposed to activities based on the social influences model, even in the absence of a statewide legislative initiative. In addition, we hypothesized that there would be state by year interactions for these variables, since social influences educational activities were the major focus of the statewide intervention effort sponsored by the Minnesota legislation. Consistent with our hypotheses, the data in Table 3 and Panels l-3 in Fig. 1 show that the level of exposure to social influences activities was quite similar in Minnesota and Wisconsin in 1986 and 1987, and that exposure subsequently increased more in Minnesota than in Wisconsin. This pattern was seen for two of the three social influences variables, activities and peer-led activities, which gave highly significant state by year interactions (F’s = 4.56 and 3.57; df = 4,438; P’s = 0.0013 and 0.0070). This pattern was not seen for discussions, where there was a significant average difference favoring Minnesota (2.32 vs 2.01; F = 34.96; df = 1,438; P = O.OOOl), as well as an increase over time in both states (F = 3.07; df = 4,438; P = 0.0163), but where the state by year interaction was not significant. The interactions for activities and peer-led activities are presented in Panels 2 and 3 in Fig. 1. Smoking
The smoking prevalence data did not support our hypothesis that the statewide initiative would result in lower adolescent tobacco use in Minnesota. Table 3 and Fig. 2 present the state by year prevalence rates for weekly smoking, standardized for age and gender. While there was a 2.4% net decline in Minnesota compared with Wisconsin from 1986 to 1990 (Panel 1 of Fig. 2), this net decline was not significant (F = 1.17; df = 4,438; P = 0.3238). Consistent with the observation that Minnesota adolescents enjoyed an environment with significantly fewer smoking models than their counterparts in Wisconsin, the main effect for state was significant: Minnesota had a lower average prevalence of smoking than Wisconsin over the 5-year study period (12.6% vs 16.1%; F = 28.80; df = 1,438; P = 0.0001). These results were corroborated by parallel analyses of the expired-air carbon monoxide data. Smokeless
The analyses were repeated for measures of educational exposure and tobacco use related to smokeless tobacco, restricting the sample to males since few females in this sample had ever used smokeless tobacco. The results for the smokeless tobacco measures were consistent with those for the smoking measures,
Panel 1: Weekly Smoking Prevalence Two State Comparison Study “I
Panel 2: Weekly Smoklng Incidence Four Group Comparison Study
Panel 3: Weekly Smoklng Prevalence Four Group Comparison Study
FIG. 2. Smoking outcomes.
except that there was a substantial use in 1990 in both states.
decline in the prevalence of smokeless tobacco
THE FOUR GROUP
The Four Group Comparison Study employed a nested cohort design (12). In 1986, 12 sampling units, defined below, were randomized to each of four conditions. The cohort of students who would be seventh graders during the 1987-1988 school year participated in a baseline survey as sixth graders in the spring of 1987. During the next school year, those students participated in one of three special interventions or in the school’s existing tobacco education program, consistent with their school’s treatment assignment. The cohort was surveyed again each spring in 1988, 1989, and 1990. Hypotheses
This study was structured to provide a more internally valid assessment of the school-based social influences programs sponsored by the Minnesota legislation than could be obtained from the Two State Comparison Study. Here school units were randomized to receive one of the three programs which were being most widely adopted across the state or to an existing curriculum condition in which the schools pledged not to adopt any of those three programs; this design avoided the selection biases inherent in the Minnesota vs Wisconsin comparison. We hypothesized that (a) the level of exposure to social influences activities in the existing curriculum condition would be lower than that seen across Minnesota in the Two State Comparison Study, (b) the level of exposure to social influences activities in the other conditions would be similar to that seen across Minnesota and higher than that seen in the existing curriculum condition, and (c) the tobacco-use incidence and prevalence rates in the three social influences conditions would be lower than that in the existing curriculum group and, for the prevalence rate, similar to that seen across Minnesota in the Two State Comparison Study. Power
We hypothesized that the most effective of the middle school intervention programs would result in a 50% reduction in incidence of weekly smoking by the end of the ninth grade, or a cumulative incidence rate of 4.5% in that condition compared with 9.0% in the existing curriculum condition (9). We hypothesized that the other intervention programs would have intermediate cumulative incidence rates. Given estimates for the within-school dependence in the data due to cluster randomization (intraclass correlation coefficient of 0.02) and for the variance reduction expected from covariance adjustments (25%), two-tailed tests, and a Type I error rate of 5% and power of 80%, we estimated that usable data from 90 students from each of 12 sampling units per condition would be required to detect these treatment effects with a hierarchical ANCOVA (9, 12).
One of the goals in the Four Group Comparison Study was to employ a sample which represented the entire seventh grade enrollment in Minnesota. As a result, we developed a sampling plan that gave each seventh grade student in the state a roughly equal chance of selection. Parallel with our work in the Two State Comparison Study, we defined a range for the size of an artificial sampling unit such that: (a) the largest unit would be no more than twice the size of the smallest unit and (b) the average expected unit size would be 39% larger than the required unit size obtained from the power analysis to allow for absent students, incomplete data, deviations in observed school enrollments from the estimates used in drawing the sample, refusals, and a 25% attrition rate between the post-test and the 2-year follow-up survey. This approach called for sampling units ranging from 88 to 176 students, each with an average expected size of 125. Sampling units were created in a fashion parallel to described for the Two State Comparison Study.5 From the 478 public schools in Minnesota that included seventh graders, 390 sampling units were created. These units were listed in random order and invited in sequence to participate in the Four Group Comparison Study. When a unit declined participation, the next unit on the randomized list was invited. School Recruitment
Recruitment procedures were similar to those used in the Two State Comparison Study, beginning with a letter to the superintendent. Given the more substantial commitment required for the Four Group Comparison Study, the followup phone call was used to seek an appointment to present the study proposal to the district. When the discussions were complete, a written agreement was signed by the PI and by the superintendent to confirm their negotiated responsibilities for the project. Survey Operations
The procedures, materials, and staff were identical across the four surveys. Scheduling. Scheduling procedures were quite similar to those used in the Two State Comparison Study, with schools in a similar geographic area surveyed in the same week. The random assignment of sampling units to conditions helped avoid any confounding of treatment condition with the survey schedule and all surveys were conducted in April and May. Surveys were conducted in the classrooms used for a required course in the targeted grade. Consent mailing and survey procedures. The consent and survey procedures in the Four Group Comparison Study were identical to those used in the Two State Comparison Study with one important distinction: in the Four Group Comparison Study the survey was confidential while in the Two State Comparison Study it ’ Even when a sampling unit required only a fraction of a school’s enrollment, the entire enrollment participated both in the annual surveys and in the appropriate education program in the seventh grade. Schools with enrollments below 25 were excluded; they accounted for less than 1% of the total enrollment in the seventh grade statewide.
was anonymous. This allowed tracking of individual in the Four Group Comparison Study. Variables
of interest and their measures,
and quality Comparison
members of the study cohort
The questionnaire to those used in the Two State
and quality control.
Treatment conditions. The three interventions selected for evaluation in the Four Group Comparison Study were identified in collaboration with the Minnesota Department of Education as those which were most likely to be widely adopted in response to the Minnesota Legislature’s initiative. The Minnesota Smoking Prevention Program is a six-lesson curriculum based on the social influences model; previous studies have found that the Minnesota Smoking Prevention Program reduced smoking onset by 75% after 2 years and by 40% after 4 years (6). The Smoke Free Generation program is a three-lesson curriculum patterned after the Minnesota Smoking Prevention Program but in a shorter form; it also used T-shirts, posters, and similar promotional items to encourage nonsmoking. The Minnesota Department of Education’s Guidelines were developed by the Department of Education and provide written guidelines and a workshop to help teachers adapt existing programs to incorporate components of the social influences model. Teacher training. Separate teacher training workshops were held for the seventh grade teachers from the schools assigned to the Minnesota Smoking Prevention Program and Minnesota Department of Education Guidelines. These statewide workshops were arranged by the Department of Education as part of its ongoing effort to assist districts statewide to adopt programs based on the social influences model; project staff assisted with all workshops. Teachers in schools assigned to the Smoke Free Generation received a 2-hr instructional videotape along with their curricular materials. No further training was provided for this condition. Quality control. A member of the project staff visited each study school over the course of the 1987-1988 school year to observe smoking education classes. Just over 90% of the health teachers in the 81 schools were observed once. The observer used an evaluation form to score each teacher on general teaching skills and style, as well as on the degree to which the material and activities used during the observation matched the components of the social influences model (18). The observer gave feedback as needed to optimize the delivery of the intervention. Analysis
We accounted for the extra component of variation due to the nested design of the Four Group Comparison Study through a mixed model ANCOVA, analyzing each wave of follow-up data with adjustment for baseline covariates. A hierarchical model was used in which students were nested within units and units were nested within treatment conditions; students and units were treated as random effects while treatment condition was treated as a fixed effect. The comparisons of interest were made by comparing the mean square for treatment against the
TABLE 4 SCHOOL AND STUDENT PARTICIPATION IN THE FOUR GROUP COMPARISON STUDY Year
Schools selected Schools participating % participating Students eligible % participating % participating % participating
1987-1988 1988 1989 1990
Sixth to seventh Seventh Eighth Ninth
94.5 83.6 77.6
96.3 85.5 79.8
97.0 88.4 81.4
95.0 85.5 81.1
Total 112” 81 72.3 7,180 95.8 85.9 80.1
Note. MSPP, Minnesota Smoking Prevention Program; SFG, Smoke Free Generation; MDEG, Minnesota Department of Education Guidelines; EC, existing curriculum. o Schools were not randomized to treatment conditions until after they had agreed to be randomized to any of the study conditions.
mean square for unit within treatment. This strategy yields unbiased tests for treatment effects and provides the statistical basis necessary to generalize any findings to the populations from which the sampled students and units were drawn (12).
Separate analyses were conducted to identify baseline confounders and covariates for the follow-up analyses. Age, gender, and self-report data on smoking patterns by the student’s father, mother, older siblings, best friend, peer group, and other students in the same grade at school were dichotomized and the two groups defined by the dichotomy were compared for differences on each outcome variable using a Pearson x2 test. Variables which were related to a dependent variable were included as covariates in the ANCOVA’s for the outcome variables. Results Participation
Of the 112 schools (teaching seventh grade) invited to participate, 81 (72.3%) agreed to do so. These schools, fed by 138 sixth grade buildings, represented 74 school districts and comprised 48 sampling units. A total of 8,992 students were enrolled in the sixth grade in April 1987 and were eligible for the baseline survey; 8,271 (92.0%) participated. Of that number, 7,180 were enrolled in the seventh grade in April 1988 and define the cohort eligible for the post-test and follow-up surveys.6 Table 4 summarizes the participation, by treatment condition, in the post-test and follow-up surveys. 6 The cohort was defined on the basis of enrollment in the appropriate school in April 1988 since the interventions were delivered during the 1987-1988 school year. Many of the students who participated in the pretest survey were not enrolled in the study schools as seventh graders and could not be enrolled in the study. The larger number was included in the pretest survey because it was impossible to identify in advance those children who would be enrolled in the study schools during the seventh grade.
Table 5 summarizes the baseline characteristics of the four conditions, with separate presentation for those included in the ninth grade follow-up survey and those lost to follow-up through the ninth grade. These data were analyzed by ANOVA, with main effects for treatment condition and follow-up status, their interaction, and a nested random effect representing sampling unit within treatment condition; the last was used as the error term to evaluate the other effects. There were no significant differences among the four conditions, either among those retained in the analysis or among those lost to follow-up at ninth grade, providing substantial assurance that differential attrition did not threaten the internal validity of the study. Those lost to follow-up were on average 24 days older (F = 7.47; df = 1,88; P = 0.0076) and were more likely to report smoking by their father (39.3% vs 30.7%; F = 12.98; df = 1,88; P = O.OOOS), mother (38.4% vs 25.1%; F = 34.82; df = 1,88; P = O.OOOl>, older siblings (17.8% vs 12.5%; F = 9.80; df = 1,88; P = 0.0024), and best friend (11.3% vs 5.9%; F = 11.18, df = 1,88; P = 0.0012), confirming that those lost to follow-up were at greater risk for becoming regular adult smokers than those who remained in the follow-up samples. Exposure
Traditional educational activities were not part of any of the three middleschool intervention programs evaluated in the Four Group Comparison study, and we did not hypothesize that there would be any condition by year interactions for these variables. As expected, there were no significant differences among the four conditions at any point in the study in the measures of exposure to traditional tobacco-use educational activities. Exposure levels to the traditional activities were high, with most students reporting exposure to between two and three of the four activities included in each measure. Exposure to long-term health content
TABLE 5 RELATED TO CIGARETTE COMPARISON STUDY
FOR THE FOUR
Included in the ninth grade follow-up
Sample size Gender (% male) Age (years) Weekly smoking prevalence Perceived smoking rates among models (%) Father Mother Older siblings Best friend Any friends Age mates at school
1,266 50.0 11.8 1.4
1,352 51.0 11.8 1.8
29.4 25.1 12.1 6.0 24.2 21.5
35.1 24.5 13.4 8.1 29.5 23.1
Lost to follow-up at ninth grade EC
1,634 49.5 11.7 1.3
1,489 51.5 11.8 0.6
278 48.6 11.8 3.5
271 48.5 11.9 2.1
315 52.5 11.8 3.8
258 58.1 11.8 1.5
29.8 25.1 12.3 4.5 19.3 19.8
28.1 24.4 12.2 4.2 23.1 18.7
31.9 40.4 16.5 11.4 28.6 28.2
38.3 35.1 15.5 10.2 32.8 19.6
44.4 41.1 19.0 14.1 36.1 27.2
36.8 36.9 20.3 9.4 29.9 24.5
Note. MSPP, Minnesota Smoking Prevention Program; SFG, Smoke Free Generation; partment of Education Guidelines; EC, existing curriculum.
was typical of the four measures of exposure to traditional tobacco education activities, and the condition by year patterns are shown in Panel 4 of Fig. 1. The means are shown in Table 6. Exposure
to Social Influences
We planned to use the exposure measures for social influences activities to assess the extent to which the students in the control group were exposed to such activities, either through other aspects of the statewide program or through their school’s adoption of another curriculum. We also hypothesized that there would be condition by year interactions for these variables, since social influences activities were a central component of the three special intervention conditions. The data did not support the first exposure hypothesis. As seen in Tables 3 and 6, the average scores for discussions, activities, and peer-led activities were higher in the existing curriculum group than in Minnesota as a whole. Our attempt to create a randomized control group that would receive less social influences programming than the rest of the state clearly did not succeed. The results for the second exposure hypothesis were mixed. The three social influences conditions did have higher exposure scores than the existing curriculum condition, but only the Minnesota Smoking Prevention Program produced scores that were reliably higher in every instance (Table 6). Further, the three social influences conditions did not mimic the state of Minnesota as a whole, but instead had substantially higher exposure scores. Thus our attempt to create randomized intervention groups that reflected the experience of the state of Minnesota as a whole also failed. TABLE ADJUSTED
MEANS FOR DEPENDENT VARIABLES RELATED FOUR GROUP COMPARISON STUDY
3.18 3.09 2.76 3.01
3.16 3.04 2.13 2.98
2.96 2.82 2.48 2.74
2.87 2.72 2.45 2.63
Self-reported exposure to traditional content (u) Long-term health Short-term health Pregnancy Smoking as a habit Self-reported exposure to social influences content (O-5) Discussions”
Self-reported weekly smoking Prevalence Incidence
Note. MSPP, Minnesota Smoking Prevention Program; SFG, Smoke Free Generation; MDEG, Minnesota Department of Education Guidelines; EC, existing curriculum. LIGroups which do not share a common underline were significantly different at P < 0.05.
The results for smoking incidence and prevalence failed to support the study hypotheses as well. Figure 2 and Table 6 present the adjusted incidence of new weekly smoking among baseline nonsmokers (Panel 2) and the adjusted prevalence of weekly smoking among all respondents (Panel 3). There were no significant differences among the four conditions on either measure at any follow-up. These results were corroborated by parallel analyses of the expired-air carbon monoxide data. A direct comparison was made between the ninth grade smoking prevalence data obtained from the Four Group Comparison Study in 1990 and the ninth grade smoking prevalence data obtained from the Two State Comparison Study in 1990, with adjustment for the age differences caused by the differences in the survey schedules for the two studies. This analysis revealed that the none of the four conditions in the Four Group Comparison Study differed from those in Minnesota as a whole, while all had significantly lower smoking prevalence rates than those in Wisconsin. Smokeless
Parallel analyses were conducted for prevalence and incidence measures of smokeless tobacco use, with the analyses again restricted to males. The findings for smokeless tobacco paralleled those for smoking: no differences in exposure to traditional educational content among the four conditions; differences favoring the social influences conditions and, particularly in the Minnesota Smoking Prevention Program, in exposure to social influences content; and no differences in prevalence or incidence for smokeless tobacco products. DISCUSSION
Consider first the results from the Two State Comparison Study. As planned, the study participants represented ninth graders in public schools in Minnesota and Wisconsin, with high participation by schools (88.1%) and students (92.6%). Wisconsin adolescents were at higher risk for tobacco use over the course of the study, as evidenced by the consistently higher tobacco use rates which they reported among their parents, siblings, friends, and peers. There was no change in the level of traditional tobacco-use education over the course of the study, in either Minnesota or Wisconsin. Beginning in 1988, there was a net increase in Minnesota adolescents’ exposure to social influences tobacco-use educational activities compared with Wisconsin, but the increase was both modest and shortlived, and exposure to social influences activities never reached levels comparable to those reported for the traditional activities. Tobacco-use prevalence was uniformly higher in Wisconsin, where weekly smoking averaged 16.1%, compared with Minnesota, where it averaged 12.6%. Finally, the 2.4% net decline in Minnesota relative to Wisconsin from 1986 to 1990 was within the range of chance variation. As a result, there is insufficient evidence to conclude that the Minnesota Legislature’s initiative reduced tobacco use among adolescents in Minnesota relative to Wisconsin over the 5 years of the study.
Consider now the results from the Four Group Comparison Study. Participating schools were more representative of their state than in any previously published tobacco-use prevention study, the four conditions were similar at baseline, and participation and follow-up rates were relatively high. Schools that adopted the Minnesota Smoking Prevention Program achieved the highest student exposure to content based on the social influences model and reached levels comparable to traditional content. The two other social influences programs achieved intermediate levels or were comparable to the existing curriculum control group. All four groups were higher in their exposure to social influences activities compared with the state of Minnesota as a whole. Even so, there were no differences in tobaccouse prevalence at the end of the study either among the four conditions or between them and the state of Minnesota as a whole, nor were there any differences among the four conditions in tobacco-use incidence. As a result, there is insufficient evidence to conclude either that any of the three social influences programs, disseminated across Minnesota in this manner, was more effective in reducing tobacco use over the 2-year follow-up period compared with the existing curriculum control condition, or than any of the four study conditions was more effective than the broader statewide effort to reduce adolescent tobacco use. Taken together, these results indicate that this legislative initiative was insufficient to reduce adolescent tobacco use statewide during the S-year study period. Given that the outcome is so clear, we must consider why the study hypotheses were not supported. Here, there are at least three possible explanations: it may reflect a failure of design, of implementation, or of the particular social influences interventions employed in the studies. Failure
Consider first the possibility of a failure of design. The design of the Two State Comparison Study, taken alone, is relatively weak, since there are many factors that could cause a change in adolescent tobacco use rates in Minnesota relative to Wisconsin independent of the Minnesota Legislature’s initiative. On the other hand, the design of the Four Group Comparison Study, taken alone, is quite strong, with random selection of school districts from across the state to participate in the study, random assignment of those districts to study conditions, and an analysis plan which accounted for the within-cluster dependence in the data. The real strength of the Minnesota-Wisconsin Adolescent Tobacco Use Research Project comes from the two designs taken together: given a consistent pattern of results, it is difficult to suggest design flaws which could account for the findings, save one: we may not have included a sufficient follow-up period in the design. We allowed for a 2-year follow-up period in the Four Group Comparison Study because previous studies have reported significant program effects at that point, and it is not likely that a longer follow-up of the Four Group Comparison Study cohort would yield a different result. We allowed for a 3-year follow-up period in the Two State Comparison Study because we suspected that it would take some time for districts across the state to implement fully the five components defined by the legislature. In hindsight, it is clear that even more time is required for full implementation of all five components, particularly the K-12 curriculum and the
smoke-free policies; even the targeted intervention in middle school takes more time to become fully established when attempted on such a large scale. Thus the failure to detect effects during the 5 years of the Two State Comparison Study may be due in part to a failure to design an adequate follow-up period. This possibility is supported by the data, which showed a net decline of 2.4% in Minnesota relative to Wisconsin over the course of the follow-up. At that rate, the expected decline of 5% would require 6 years of follow-up rather than the three that were included in the design. Failure
Consider next the possibility of a failure of implementation. Implementation failure could occur at the level of the design, at the level of power, or at the level of the intervention. There is little evidence of a failure of design implementation in the Two State Comparison Study, since the design was carried out as planned, with consistently high participation by schools and students, and with the same survey instruments, methods, and staff throughout the study. Further, there is little evidence of contamination in the Two State Study, where the measures of exposure to social influences content suggested that such exposure was uniformly low in Wisconsin and that it did not change over the period of the study. There is a greater possibility for a failure of design implementation in the Four Group Comparison Study, particularly in the area of contamination or compensatory rivalry (21). We note for example that the exposure levels for social influences programming were substantially higher in the existing curriculum control group than across Minnesota as a whole (Panels 2,3,5, and 6 in Fig. l), suggesting that these students were exposed to a level that was above and beyond that received by students in nonstudy schools across the same state; such exposure may have reduced differences among the four study conditions. We know that these schools did not use any of the three programs which comprised the three special intervention conditions, but did not try to limit further what they did in their classrooms. These districts may well have adopted other activities that included components of the social influences model, contaminating this condition and preventing us from comparing the three special intervention conditions with a real control condition. Thus design implementation failure must be considered, at least for the Four Group Comparison Study. A post hoc review of the power calculations revealed that we had overestimated the within-unit dependence in the data for the Two State Comparison Study and that there was sufficient power to detect an even smaller difference than we had planned for: a net decline in smoking prevalence of 3.8%. A similar review for the Four Group Comparison Study revealed that we had slightly underestimated within unit dependence in the data for incidence and that there was sufficient power to detect only a slightly larger difference than we had planned for: a net difference in smoking incidence of 5.1%. Even with the small underestimation for the incidence analysis, the results from the two studies cannot be viewed as an artifact of inadequate power. Evidence on the quality of the intervention implementation comes from several
sources. The educational exposure data were drawn from self-report items that had face validity and Cronbach (Yscores in the acceptable range (all above 0.70 by ninth grade). The lack of any substantial separation between Minnesota and Wisconsin in their exposure to social influences programming based on these measures is consistent with a failure of intervention implementation in the Two State Comparison Study (Panels 5 and 6 in Fig. 1). A dose-response analysis of the Two State Comparison Study exposure adds further support to this interpretation. This analysis revealed a significant relationship between the dose of social influences activities and the relative odds of weekly smoking and predicted that the average dose received in Minnesota would be insufficient to produce a significant decline in smoking prevalence.7 At the same time, there was separation on the educational exposure measures among the four conditions in the Four Group Comparison Study, but still no differences in tobacco-use incidence or prevalence rates, nor was there evidence of a dose-response relationship in the Four Group Comparison Study data set. Thus the educational exposure data support a failure of intervention implementation in the Two State Comparison Study but not in the Four Group Comparison Study. We must note, however, that we have no experience with these measures from previous studies and so cannot determine whether the exposure levels achieved in the Four Group Comparison Study were as high as we have achieved in previous studies of the Minnesota Smoking Prevention Program; as a result, we cannot be sure that the implementation of the interventions in the Four Group Comparison Study was as strong as in our previous investigations, leaving open the question of intervention implementation failure. Another source of evidence on the quality of the intervention implementation comes from the records maintained by the Minnesota Department of Education. These records indicated that the Minnesota Smoking Prevention Program, which produced the highest exposure to the social influences program, was used by approximately 50% of the state’s school districts at some point in the sixth to eighth grades, while other activities, which would be expected to produce lower exposure, were used by the remaining districts in the state. These data are also consistent with a failure of intervention implementation in the Two State Comparison Study, though they are not helpful in the interpretation of the Four Group Comparison Study. A third source of evidence on the quality of the intervention implementation is anecdotal and based on discussions with officials in the Department of Education. They expressed concern early on that the advent of the AIDS crisis and the Legislature’s subsequent mandate to school districts to adopt AIDS risk reduction programs, together with similar pressure to increase drug use prevention programming, may have combined to restrict the time and energy which teachers could put into tobacco-use prevention. These officials also indicated that many ’ We note however that this dose-response association may have been an artifact of measuring dose and response in the same questionnaire, in the same population, and at the same time. We regret that we have no means by which to distinguish what part of this association may be real and what part may be artifactual.
teachers and administrators believed that smoking was declining even without their efforts, that they had already done a great deal in this area, and that other issues were of greater importance for their students. None of these developments would favor high quality implementation of tobacco-use prevention programming during the study period and are consistent with intervention implementation failure in both the Two State Comparison Study and the Four Group Comparison Study. The final source of evidence on the quality of the intervention implementation comes from the tobacco use results themselves, at least in the Four Group Comparison Study. We note that the four study conditions presented an average incidence rate of 9%, or exactly what we had expected in the existing curriculum control condition. None of the social influences interventions presented rates approaching the 4.5% which had been predicted based on earlier studies. These data are also consistent with inadequate implementation of the interventions in the Four Group Comparison Study. Based on this evidence, we are inclined to give considerable credence to intervention implementation failure as a possible explanation for the results from the Two State Comparison Study: the states’s school districts may not have adopted effective programs in sufficient numbers and may not have implemented them with sufficient fidelity to produce a reduction in adolescent tobacco use within the 3-year follow-up period provided by the design. We are also inclined to give some credence to this explanation of the Four Group Comparison Study findings: in spite of the perceptions that the training went well and in spite of the classroom observation data which suggested that teachers in at least the Minnesota Smoking Prevention Program condition were adhering to that curriculum, there is evidence that teachers may not have spent sufficient time on tobacco prevention, given the pressures to address other important health education issues. Failure
of the Specific Interventions
Consider next the possibility of a failure of the particular social influences interventions which were employed in these studies. Based on the substantial and growing evidence suggesting that interventions based on the social influences model can reduce adolescent tobacco use, at least in controlled studies (24, 22), and given our own positive findings with the Minnesota Smoking Prevention Program in previous studies, this would not seem a likely explanation. Yet there are several other factors which must be considered. First, there have been no previous evaluations of two of the social influences interventions employed in these studies, the Smoke Free Generation and the Minnesota Department of Education Guidelines, and it may be that they are insufficient to deliver the messages and skills which define the social influences model. Second, most of the previously published studies on the social influences model, including ours, suffered from several of the methodological problems common to the field (4), particularly the failure to adequately reflect cluster randomization in the analysis. If we had ignored the clustering in the Two State Comparison Study, we would have reported a significant test result (F = 3.38; u” = 4,35093; P = 0.0091) and probably would have interpreted the 2.4% net decline in Minnesota compared
with that in Wisconsin as indicating that the Minnesota Legislature’s initiative had been successful. With the correct analysis, we must of course draw a different conclusion. Third, many investigators in the field have recognized that there are clear limits, particularly in the maintenance of effects, to what can be achieved with school-based programs and have moved to incorporate other intervention strategies, often at the community level, to extend the impact of the social influences model (e.g., 23, 24). Our own most recent study of the Minnesota Smoking Prevention Program, in the context of a broad community-based heart disease prevention trial, revealed the largest and most durable effects on adolescent tobacco use reported to date (8). Though the Minnesota Legislature’s initiative supported several broader interventions in addition to the school-based programs, the intensity of those interventions was certainly far below that achieved in these more focused community studies. Thus the results from the Two State Comparison Study and the Four Group Comparison Study may be due in part to inadequacies in one or more of the particular social influences programs employed and quite likely to the insufficiency of the total effort delivered in Minnesota as a result of the Legislature’s initiative. CONCLUSION
Our findings are likely due to a combination of these factors. In terms of the Four Group Comparison Study, the lack of any evidence that the social influences interventions were any more effective than the existing curriculum control condition is probably attributable to a combination of contamination or compensatory rivalry in the existing curriculum control condition and inadequate implementation in the intervention conditions. In terms of the Two State Comparison Study, the modest net decline is probably attributable to inadequate implementation of the social influences programs in Minnesota, inadequate follow-up in both states, and inadequate intensity of the entire statewide effort. It may simply take a more intense effort over a longer time than occurred in this instance to achieve statewide reductions in adolescent tobacco use. The two other ongoing dissemination studies (10, 11) will provide additional information on this question, and we look forward to their results. ACKNOWLEDGMENTS The authors thank the staff and students in the hundreds of Minnesota and Wisconsin public school districts that participated in the study. The authors also thank Mr. Chet Bradley of the Wisconsin Department of Public Instruction and Ms. Nancy Kaufman and Dr. Doug Piper of the Wisconsin Department of Health and Social Services, who provided valuable assistance throughout the study; Ms. Jan Whitbeck, who directed the surveys; Mr. Peter Hannan, who helped with the power analyses; and Ms. Laurie Zurbey, who served as principal secretary for the project.
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