LETTERS REGARDING DRIVING AFTER DRUG AND ALCOHOL USE AMONG US HIGH SCHOOL SENIORS We read with interest the article by O’Malley and Johnston examining trends in the proportion of US high school seniors who drive after using drugs or ride in vehicles whose driver has used drugs.1 We commend the authors for investigating the correlates of these behaviors; however, we have some concerns. The authors use data from Monitoring the Future (MTF) for the years 2001---2011. We are interested to know the final sample size for this study. The authors rightly state that MTF surveys approximately 17 000 12th graders and questions assessing substance use and driving were distributed to one sixth of the total sample. However, this does not provide a precise number of observations used in this study. Inclusion or exclusion criteria are not included, despite the fact that a large data set would surely contain observations requiring exclusion. Finally, MTF also samples 10th grade students, an age group able to receive a driver’s license. We wonder why the authors did not include participants from this grade. The rationale for inclusion of measures in the current study cites work conducted by the
Letters to the editor referring to a recent Journal article are encouraged up to 3 months after the article's appearance. By submitting a letter to the editor, the author gives permission for its publication in the Journal. Letters should not duplicate material being published or submitted elsewhere. The editors reserve the right to edit and abridge letters and to publish responses. Text is limited to 400 words and 10 references. Submit online at www. editorialmanager.com/ajph for immediate Web posting, or at ajph.edmgr.com for later print publication. Online responses are automatically considered for print publication. Queries should be addressed to the Editor-in-Chief, Mary E. Northridge, PhD, MPH, at [email protected].
authors using earlier years of MTF and may overlook variables demonstrating associations with adolescent substance use in other nationally representative studies. For example, parental and peer alcohol consumption have demonstrated associations with impaired driving in studies from the National Longitudinal Study of Adolescent Health (Add Health).2 Risk factors such as these, which were found to be associated in more recent literature, may have been worth including. Additionally, Add Health found risk factors for impaired driving vary by race/ethnicity.3 Given that O’Malley and Johnston report racial differences in the effect of some risk factors, including religious commitment and miles driven, the potential effect modification of race/ethnicity between the measures and driving after using drugs would have been interesting to explore. Moreover, the variables included in their study could conceivably be correlated, and it is unclear if the authors investigated this possible collinearity. Because the sample size is not provided in the article, it is difficult to know how large the effect of collinearity would be on the estimates. Finally, while the authors note the possible limitation of absenteeism on the results, we wonder if the authors considered additional limitations and potential selection bias incurred by use of a school-based sample. Specifically, are these results generalizable to students who are home-schooled, attend private school, or have dropped out of school completely? j Abenaa Acheampong, BS Chukwuemeka Okafor, MPH Joy D. Scheidell, MPH
About the Authors All authors are in the Department of Epidemiology, College of Public Health and Health Profession, College of Medicine, University of Florida, Gainesville. Correspondence should be sent to Joy D. Scheidell, 2004 Mowry Road PO Box 100231, Gainesville, Florida 32610 (e-mail: jdbscheidell722@ufl.edu). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link.
April 2014, Vol 104, No. 4 | American Journal of Public Health
This letter was accepted December 8, 2013. doi:10.2105/AJPH.2013.301839
Contributors All authors contributed to the conception and content of the letter. J. D. Scheidell wrote the initial draft. A. Acheampong and C. Okafor wrote and edited subsequent drafts.
References 1. O’Malley PM, Johnston LD. Driving after drug or alcohol use by US high school seniors, 2001-2011. Am J Public Health. 2013;103(11):2027---2034. 2. Maldonado-Molina MM, Reingle JM, Delcher C, Branchini J. The role of parental alcohol consumption on driving under the influence of alcohol: results from a longitudinal, nationally representative sample. Accid Anal Prev. 2011;43(6):2182---2187. 3. Delcher C, Johnson R, Maldonado-Molina MM. Driving after drinking among young adults of different race/ethnicities in the United States: unique risk factors in early adolescence? J Adolesc Health. 2013;52(5): 584---591.
O’MALLEY AND JOHNSTON RESPOND We appreciate Acheampong et al.’s interest in and commendation of our article. The sample size for the data presented in Table 1 is provided in a note that says the number of respondents was approximately 2000 per year. Although this does not provide a precise number, it seems to us sufficiently informative for readers and reviewers. Tables 2 and 3 provide the precise numbers of cases involved in the four logistic regressions (n = 6161, 6155, 6111, 6107). The only exclusion criterion used for study respondents was that they had to provide data for the variables used. Although not stated explicitly, this seems obvious, given that we did not mention any imputation. We did not include participants from 10th grade because Monitoring the Future (MTF) does not ask 10th graders about driving after alcohol or drug use. It is certainly true that variables other than those included in Tables 2 and 3 may be associated with driving or riding after alcohol or drug use. We included those that we considered most relevant to the purposes of the article among the very large number of measures available in the MTF study. Parental alcohol consumption is not one of those, but
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peer consumption of alcohol is, along with peer consumption of a variety of other substances. Also available are measures of age, academic program, delinquency, vandalism, risk-taking, self-esteem, personal disapproval of substance use, public versus private school, and many others. We believe that the set of predictors we chose to include provided a very reasonable selection. We could have explored interactions, including those by race/ethnicity. Indeed, we have shown that race/ethnicity interacts with parental education and with religious commitment in associations with substance use.1---3 It is likely that race/ethnicity would interact with other variables as well, such as urbanicity. Other variables such as gender or hours worked per week might have interactions in associations with driving or riding. A thorough investigation of all possible or even likely interactions among the 12 independent variables in the logistic models would be beyond the scope of the article. (The article is at the Journal’s word count limit.) Use of a school-based sample clearly limits the sample to school students only (both public and private schools were included); homeschooled 12th graders and high school dropouts are not eligible and therefore the findings cannot be assumed to hold for those populations. The relevant population is high school seniors, and we were careful to make that clear throughout the article, including in the title. j
substance use among US 8th-, 10th-, and 12th-grade students: findings from the Monitoring the Future project. J Stud Alcohol Drugs. 2011;72(2):279---285. 2. Wallace JM Jr, Delva J, O’Malley PM, et al. Race/ ethnicity, religiosity and adolescent alcohol, cigarette and marijuana use. Soc Work Public Health. 2007;23: 193---213. 3. Wallace JM Jr, Vaughn MG, Bachman JG, O’Malley PM, Johnston LD, Schulenberg JE. Race/ethnicity, socioeconomic factors, and smoking among early adolescent girls in the United States. Drug Alcohol Depend. 2009; 104(suppl 1):S42---S49.
Patrick M. O’Malley, PhD Lloyd D. Johnston, PhD
About the Authors Patrick M. O’Malley and Lloyd D. Johnston are with the Survey Research Center, Institute for Social Research, University of Michigan, Ann Arbor. Correspondence should be sent to Patrick M. O’Malley, 2320 ISR, 426 Thompson Street, Ann Arbor, Michigan 48104 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted December 17, 2013. doi:10.2105/AJPH.2013.301853
Contributors Both authors contributed equally to the letter.
References 1. Bachman JG, O’Malley PM, Johnston LD, Schulenberg JE, Wallace JM. Racial/ethnic differences in the relationship between parental education and
e8 | Letters
American Journal of Public Health | April 2014, Vol 104, No. 4
Letters to the editor referring to a recent Journal article are encouraged up to 3 months after the article's appearance. By submitting a letter to the editor, the author gives permission for its publication in the Journal. Letters should not duplicate material being published or submitted elsewhere. The editors reserve the right to edit and abridge letters and to publish responses. Text is limited to 400 words and 10 references. Submit online at www. editorialmanager.com/ajph for immediate Web posting, or at ajph.edmgr.com for later print publication. Online responses are automatically considered for print publication. Queries should be addressed to the Editor-in-Chief, Mary E. Northridge, PhD, MPH, at [email protected].
authors using earlier years of MTF and may overlook variables demonstrating associations with adolescent substance use in other nationally representative studies. For example, parental and peer alcohol consumption have demonstrated associations with impaired driving in studies from the National Longitudinal Study of Adolescent Health (Add Health).2 Risk factors such as these, which were found to be associated in more recent literature, may have been worth including. Additionally, Add Health found risk factors for impaired driving vary by race/ethnicity.3 Given that O’Malley and Johnston report racial differences in the effect of some risk factors, including religious commitment and miles driven, the potential effect modification of race/ethnicity between the measures and driving after using drugs would have been interesting to explore. Moreover, the variables included in their study could conceivably be correlated, and it is unclear if the authors investigated this possible collinearity. Because the sample size is not provided in the article, it is difficult to know how large the effect of collinearity would be on the estimates. Finally, while the authors note the possible limitation of absenteeism on the results, we wonder if the authors considered additional limitations and potential selection bias incurred by use of a school-based sample. Specifically, are these results generalizable to students who are home-schooled, attend private school, or have dropped out of school completely? j Abenaa Acheampong, BS Chukwuemeka Okafor, MPH Joy D. Scheidell, MPH
About the Authors All authors are in the Department of Epidemiology, College of Public Health and Health Profession, College of Medicine, University of Florida, Gainesville. Correspondence should be sent to Joy D. Scheidell, 2004 Mowry Road PO Box 100231, Gainesville, Florida 32610 (e-mail: jdbscheidell722@ufl.edu). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link.
April 2014, Vol 104, No. 4 | American Journal of Public Health
This letter was accepted December 8, 2013. doi:10.2105/AJPH.2013.301839
Contributors All authors contributed to the conception and content of the letter. J. D. Scheidell wrote the initial draft. A. Acheampong and C. Okafor wrote and edited subsequent drafts.
References 1. O’Malley PM, Johnston LD. Driving after drug or alcohol use by US high school seniors, 2001-2011. Am J Public Health. 2013;103(11):2027---2034. 2. Maldonado-Molina MM, Reingle JM, Delcher C, Branchini J. The role of parental alcohol consumption on driving under the influence of alcohol: results from a longitudinal, nationally representative sample. Accid Anal Prev. 2011;43(6):2182---2187. 3. Delcher C, Johnson R, Maldonado-Molina MM. Driving after drinking among young adults of different race/ethnicities in the United States: unique risk factors in early adolescence? J Adolesc Health. 2013;52(5): 584---591.
O’MALLEY AND JOHNSTON RESPOND We appreciate Acheampong et al.’s interest in and commendation of our article. The sample size for the data presented in Table 1 is provided in a note that says the number of respondents was approximately 2000 per year. Although this does not provide a precise number, it seems to us sufficiently informative for readers and reviewers. Tables 2 and 3 provide the precise numbers of cases involved in the four logistic regressions (n = 6161, 6155, 6111, 6107). The only exclusion criterion used for study respondents was that they had to provide data for the variables used. Although not stated explicitly, this seems obvious, given that we did not mention any imputation. We did not include participants from 10th grade because Monitoring the Future (MTF) does not ask 10th graders about driving after alcohol or drug use. It is certainly true that variables other than those included in Tables 2 and 3 may be associated with driving or riding after alcohol or drug use. We included those that we considered most relevant to the purposes of the article among the very large number of measures available in the MTF study. Parental alcohol consumption is not one of those, but
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LETTERS
peer consumption of alcohol is, along with peer consumption of a variety of other substances. Also available are measures of age, academic program, delinquency, vandalism, risk-taking, self-esteem, personal disapproval of substance use, public versus private school, and many others. We believe that the set of predictors we chose to include provided a very reasonable selection. We could have explored interactions, including those by race/ethnicity. Indeed, we have shown that race/ethnicity interacts with parental education and with religious commitment in associations with substance use.1---3 It is likely that race/ethnicity would interact with other variables as well, such as urbanicity. Other variables such as gender or hours worked per week might have interactions in associations with driving or riding. A thorough investigation of all possible or even likely interactions among the 12 independent variables in the logistic models would be beyond the scope of the article. (The article is at the Journal’s word count limit.) Use of a school-based sample clearly limits the sample to school students only (both public and private schools were included); homeschooled 12th graders and high school dropouts are not eligible and therefore the findings cannot be assumed to hold for those populations. The relevant population is high school seniors, and we were careful to make that clear throughout the article, including in the title. j
substance use among US 8th-, 10th-, and 12th-grade students: findings from the Monitoring the Future project. J Stud Alcohol Drugs. 2011;72(2):279---285. 2. Wallace JM Jr, Delva J, O’Malley PM, et al. Race/ ethnicity, religiosity and adolescent alcohol, cigarette and marijuana use. Soc Work Public Health. 2007;23: 193---213. 3. Wallace JM Jr, Vaughn MG, Bachman JG, O’Malley PM, Johnston LD, Schulenberg JE. Race/ethnicity, socioeconomic factors, and smoking among early adolescent girls in the United States. Drug Alcohol Depend. 2009; 104(suppl 1):S42---S49.
Patrick M. O’Malley, PhD Lloyd D. Johnston, PhD
About the Authors Patrick M. O’Malley and Lloyd D. Johnston are with the Survey Research Center, Institute for Social Research, University of Michigan, Ann Arbor. Correspondence should be sent to Patrick M. O’Malley, 2320 ISR, 426 Thompson Street, Ann Arbor, Michigan 48104 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This letter was accepted December 17, 2013. doi:10.2105/AJPH.2013.301853
Contributors Both authors contributed equally to the letter.
References 1. Bachman JG, O’Malley PM, Johnston LD, Schulenberg JE, Wallace JM. Racial/ethnic differences in the relationship between parental education and
e8 | Letters
American Journal of Public Health | April 2014, Vol 104, No. 4
