Measuring Depressive Symptomatology in a General Population Monica D. Blumenthal, MD, PhD
Three hundred twenty respondents in selected geographic interviewed with a structured questionnaire that included the Zung Self-Rating Depression Scale. Dimensional analysis indicates that some items are not pure measures of the areas were
constructs they were originally intended to assess. Moreover, some of the dimensions within the scale apparently convey different meanings to different segments in the population. In addition, different dimensions within the scale have varying demographic correlates. The analysis suggests that in order for the scale to be a truly useful device for assessing depressive symptomatology in a general population, additional items need to be added and some questions need to be followed by probes to clarify the exact frame of reference of the respondents.
for understanding any disease is an of the distribution of the illness in the general population and the variables that determine that distribution. In psychiatry such basic information is often lacking. Epidemiological information about the de¬ pressive disorders would be particularly useful since they are not only quite common, but also thought to be influ¬ enced by environmental conditions. Silverman1 has esti¬ mated that the prevalence rate for depressive psychosis is less than one per 1,000 population, and that of depres¬ sive neurosis is two or three times higher. Hordern2 cites higher rates. Others, however, working with special groups, such as nonpsychiatric, medically ill patients, find a very high prevalence of depression.35 The true preva¬ lence of the depressive disorders in the United States is not known.
requirement A understanding basic
Accepted for publication Nov 11, 1974. From the Institute for Social Research,
Arbor.
University of Michigan, Ann
Reprint requests to the Institute for Social Research, University of Michigan, Ann Arbor, MI 48106 (Dr. Blumenthal).
Blum6 has pointed out a major difficulty in studying psy¬ chiatric epidemiology. He states that the method of iden¬ tifying mental illness must have both validity and reli¬ ability. Furthermore, the validity of a diagnosis for which there are no specific laboratory tests or findings depends on the judgment of the clinician, in this case, the psychia¬ trist. Unfortunately, psychiatric diagnosis is characterized by a certain lack of reliability.711 Two of the major studies in psychiatric epidemiology, the Stirling County Study12 and the Midtown Manhattan Study,1' overcame this diffi¬ culty by utilizing psychiatric judgments based on struc¬ tured interviews. By intensively training the psychiatrists who made the disability ratings, the investigators were able to develop procedures that were sufficiently reliable to be satisfactory as research tools. Unfortunately, in choosing this methodology, both studies fail in respect to a third criterion essential to epidemiologie research, that is, that the tool used should be replicable. The device of using extensive training to ensure reliability among the psychi¬ atrists makes it difficult for others to replicate the work. The Zung Self-Rating Depression Scale (SDS) appears to have the validity, reliability, and replicability so impor¬ tant in epidemiological research. It is a 20-item scale mea¬ suring symptoms of depressive illness"15 and has had ex¬ tensive use and considerable validation. The scale is a balanced instrument. Ten of the items are worded so that positive responses indicate the presence of symptomatol¬ ogy. Each item is scored on a four-point scale "a little of the time," "some of the time," "a good part of the time," or "most of the time." Symptom-negative items are scored inversely, and all items are summed to form a total score. It will be shown later that there is some question as to whether or not items that supposedly measure symptoma¬ tology by inquiring about its absence function in the man¬ ner in which they were intended.
Downloaded From: http://archpsyc.jamanetwork.com/ by a La Trobe University User on 07/05/2016
Because the SDS has been extensively used, a consid¬ erable body of evidence has accumulated indicating that the scale has criterion validity, that is, scores on the scale are congruent with what would be expected on the basis of psychiatric diagnosis if the scale were valid. Some of these data are summarized below. Zung first used the scale on 56 psychiatric inpatients who were separated into two groups: those who were both admitted and discharged with the diagnosis of depressive disorder (DD) and those who were admitted as having a depressive disorder but discharged with another diagnosis (DO)." Scores on the SDS of the DD group were higher (mean SDS .73) than those of the DO group (mean SDS .53). (The Zung scale is scored by summing the responses to the items and di¬ viding by 80. For symptom-positive items, "most of the time" equals 4; "a good part of the time" equals 3; "some of the time" equals 2; and "a little of the time" equals 1. The score is then "normalized" according to a table con¬ structed by Zung." Some investigators then multiply the total score by 100.) However, the DO group still scored sig¬ nificantly higher than the normal control subjects who had been psychiatrically screened to rule out individuals with a depressive illness or a history of a recent depressive epi¬ sode (mean SDS .33). Later, Zung et al15 showed that outpatients who were diagnosed as having a psychoneurotic depressive disorder scored significantly higher than pa¬ tients having personality disorders, psychoneurotic anxi¬ ety reactions, and transient situational disorders of adult life, although all three outpatient groups scored higher than the normal controls of the first study. The scale has been shown to be significantly responsive to antidepressant drug treatment in hospitalized patients by some workers,1618 although others have found the scale insensitive to drug-induced change.19 Crosby20 reported that 80% of the patients with spinal and paraspinal in¬ juries scored over 43 (the top of the normal range accord¬ ing to Zung's original study) on the Zung SDS. Since de¬ pression is a common concomitant of paraplegia, Crosby's study provides some validity for the scale. Jacobs et al21 showed mean scores on the Zung SDS were significatnly higher among 50 patients selected by interns as "crocks" than in a group of patients not given such a label. This finding is of interest, since it is well known that patients with depressive illness may have multiple somatic com¬ plaints without prominent symptoms of depressed affect. Such studies indicate the Zung SDS is a useful tool in pop¬ ulations where psychiatric disorder has not been sus¬ pected. In a study of 73 alcoholic patients in an inpatient setting, patients were found to have a mean SDS index of .64,22 a figure somewhat higher than the mean SDS value Zung obtained for his DO group. Variability of depression scores in this group was considerably greater than among Zung's depressed patients. Both the high scores and the greater variability are what might be expected among al¬ coholic patients if the scale had criterion validity, since al¬ coholism is commonly associated with depressive symp¬ toms, although not all alcoholic patients are depressed. In the same study, patients also showed a significant de¬ crease in SDS scores following treatment. Cross-cultural data on the SDS23 are available for Ja¬ pan, Australia, Czechoslovakia, England, Germany, and =
=
=
Switzerland. These studies show a high degree of com¬ parability to the data available from the United States. Moreover, the correlation coefficient between global rat¬ ings made by physicians of the extent of the depression and the SDS range from .43 to .65 for all countries. Some evidence on the construct validity of the instru¬ ment is available. Zung24 found the SDS to correlate with the Depression scale of the Minnesota Multiphasic Person¬ ality Inventory with an r of .59, with the Hamilton De¬ pression Scale with an r of .56,23 with the Beck Scale with an r of .76, and with the Lubin Scale with an r of .29. In addition, the self-rating scale correlates highly (r .87) with observer ratings on the same dimensions.25 A few studies on the methodological characteristics of the scale have been made. High school students were not able to present themselves as less depressed than they actually were, although they could fake more depressed scores when instructed to do so.26 The scale is free of order ef¬ fects.27 The scale has been criticized as inadequate in its cov¬ erage of the spectrum of depressive symptomatology.28 It has also been criticized for not significantly differ¬ entiating between depressed patients located in a general practice, in day care treatment settings, and on an inpatient psychiatric service.29 It is also true that many of the components of depression are covered by a single item. Nevertheless, the scale has a very considerable valid¬ ity that would be exceedingly difficult to reproduce with¬ out extensive effort. Consequently, the SDS appears to be a good choice for the assessment of depressive symptoma¬ tology in a general population. There is a crucial methodological problem, however, that needs to be answered before the value of this instrument as a tool for a study of depression in a general population can be assessed. It is obvious from the construction of the scale that the instrument is multidimensional. Indeed, Zung designed the instrument to cover the range of symp¬ toms that are seen in depressions. Moreover, the scale had been factor analyzed and found to contain four factors.30·31 Thus, the question arises whether or not the major di¬ mensions in the scale have the same meaning for various population segments. This requirement may not seem ob¬ vious, but it can be illustrated. It is well known that the same language may be used quite differently—depending on the circumstances or the user. For example, "How are you" may be a greeting equivalent to "Hello" if it is used in passing down the hall, or it may be a serious inquiry into well-being if made by a physician of a patient. If a scale is to be used in all segments of a population, the items in the various dimensions within a scale must have the same meaning for all the population segments with which the scale is used. This report addresses itself to this =
question.
METHODS
Population Investigated One hundred sixty married couples were interviewed by profes¬ sional female interviewers in the summer of 1972 in the following locations: Lycoming, Penn; Marshall County, Ind; Louisville and Lexington, Ky; St. Joseph County, Flint, and Hancock, Mich; Day¬ ton and Butler, Ohio; and Logan County, Colo. Since the study was
Downloaded From: http://archpsyc.jamanetwork.com/ by a La Trobe University User on 07/05/2016
1.—Percentage Distribution of Selected Demographic Characteristics Among Study Respondents Table
% Men
Characteristic
(N
=
160)
Women
(N
=
160)
Total
(N
=
320)
Age 18-29 y r 30-39 yr 40-49 yr 50-59 yr
>60yr Total Race Black White Total Income
29 20 14 15
35 18 13 18
22 100
100
96 100
>$6,000 $6,000-89,999 $10,000-12,499 $12,500-$14,999 >$15,000
23 29 22 10
Total
Occupational status Currently employed Retired Laid off or unemployed Housewife Student or other Total Marital status First marriage Marriage after divorce Marriage after death of
32 19 13 16 20 100
100 74 20
29
51 11
65
32
100
100
100
85 13
83 15
84
100
100
100
11
15 16 39 15 15 100
14
previous spouse Total Education 0-8 yr 9-11 yr High school graduate Some college
16 31 16
>4yr college Total
100
48 13 12 100
meant to be primarily methodological, the sample was not de¬ signed to represent the US population or any specific region. The interviewers were assigned 10 to 20 segments (a segment is a des¬ ignated area with specified geographic boundaries containing 20 to 30 addresses within one of the Survey Research Center's pri¬ mary sampling units), given a specific geographic location marked on a map as a starting point, and instructed to proceed around each segment in a clockwise direction. The interviewers made at every third household unit until the as¬ of couples had been interviewed. If the required number of interviews could not be obtained in the first trip around the segment, the interviewer started again at the beginning of the segment, traveling in the same direction but beginning with the second house. Interviewers were required to interview from two to three couples for each two segments, depending on the size of the segment. The interviewers worked in pairs, and interviews of the couples were conducted simultaneously with the two spouses. Interviews were held in separate rooms whenever pos¬ sible (about 95% of the cases). A total of 320 married people were interviewed. The interview was a structured instrument that the inter-
requests for interviews
signed number
viewers were required to follow exactly. The interview, which lasted approximately an hour, centered mainly on the respon¬ dent's work, his marriage, and his social relationships. The inter¬ viewers recorded the answers given them and made nondirective probes. They did not rate the respondents in any way. Coding was conducted according to methods standard at the Survey Research Center.32 Table 1 shows the characteristics of the respondent
population. RESULTS
The responses to the items in the Zung SDS were inter¬ related using gammas, which are a measure of association suitable for ordinal data.33 The gamma matrix was then subjected to a Guttman-Lingoes Smallest Space Analy¬ sis.34·35 The analysis yielded three main clusters in three dimensions with a coefficient of alienation of .14 and a Kruskal stress coefficient of .12. The items within each di¬ mension were subjected to additional analysis to deter¬ mine if the relationships between items within a cluster were similar for a variety of subgroups within the popu¬ lation. The basic principle of the dimensional analysis was that items within a dimension or cluster should show consist¬ ent interitem relationships within selected demographic subgroups. If such relationships are reasonably consistent, one can assume that the items are viewed similarly by those subgroups and probably most people in the popu¬ lation. If relationships are inconsistent, the meaning of the items probably varies from group to group. This anal¬ ysis strategy for survey data is outlined in Blumenthal et al.36 The subgroups chosen as units of replication are shown in Table 2, which illustrates this type of analysis. The Table shows all the interitem correlations for those items that were contained in the largest cluster suggested by the Smallest Space Analysis, the Zung Well-Being Cluster. This cluster consists of seven of the ten positively worded items in the Zung scale: mind is as clear as it used to be find it easy to do the things I used to feel hopeful about the future find it easy to make decisions feel that I am useful and needed My life is pretty full I still enjoy the things I used to
My I I I I
Interestingly enough, these same seven items were found on the first factor in the factor analysis of data by Rickels et al30 from 831 depressed outpatients. These items are designed to be the reverse of items indicating depres¬ sive symptoms. However, their face value indicates a state of well-being. The fact that statements that are as diverse in content as the equivalent of psychomotor retardation ("I find it easy to do the things I used to") are in the same cluster with the putative equivalent of confusion ("My mind is as clear as it used to be") and hopelessness ("I feel hopeful about the future") underlines the possibility that the respondent may be reacting to the positive element in the items rather than to the specific symptom (or lack of to load
it) that the item is supposed to represent. Inspection of Table 2 shows a number of low correla¬ tions between items (gammas below .4), particularly
Downloaded From: http://archpsyc.jamanetwork.com/ by a La Trobe University User on 07/05/2016
Table
2.—Relationships All Re¬ spon¬
dents
(N) V405 Mind clear
(320) as
usual
Confi¬ dence
Zung Well-Belng Clusters for Selected Subgroups (Gammas)
Worn-
Age,
Age,
58
Educa-
Some
Previ-
tion,
College
ously
Men
en
yr
yr
Grade
(160)
(160)
(69)
(72)
(98)
(96)
.49-.75 .39-.65 .34-,62 .36-.64 .23-.53 -33-.61
.63 .59 .52 .54 .37 .52
.61 .47 .44 .46 .40 .42
.74 .63 .41 .61 .52 .53
.34 .57 .42 .29 .26 .23
.66 .51 .42 .55 .32 .55
.74 .70 .45 .53 .48 .66
.50 .42 .37 .33 .33 .44
.67 .62 .61 .56 .55 .49
,33-.59 .28-.54 .36-,64 .25-.55 .40-.68
.44 .39 .45 .37 .51
.49 .44 .54 .41 .57
.71 .45 .60 .53 .65
.16 .31 .37 .38 .35
.38 .34 .45 .48 .57
.79 .44 .64 .57 .60
.19 .36 .50 .38
.26-.S4 .43-.76 .30-.60 .35-.63
.36 .60 .38 .36
.43 .65 .50 .59
.43 .84 .69 .52
.09 .33 .24 .12
.31 .64 .45 .60
.54 .71 .66 .62
.46-.74 .35-. 5 .30-.58
.52 .56 .44
.69 .45 .43
.69 .38 .35
.47 .58 .26
.53 .49 .53
.74
.63-.91 ,48-.76
.76 .67
.77 .60
.90 .64
.63 .53
.40-.70
.58
.53
.54
.42
tion
Di-
$12,500 vorced (80) (44) (69)
Interval
Married Married >5 yr >21 yr
(90)
(136)
.56 .33 .35 .56 .17 .28
.75 .52 .28 .48 .36 .54
.44 .47 .51 .33 .21 .31
.64 .64 .55 .55 .61
.31 .40 .55 .38 .50
.63 .37 .55 .41 .66
.25 .39 .37 .35 .43
.08 .45 .13 .21
.64 .71 .68 .64
.62 .69 .65 .56
.47 .82 .54 .56
.16 .44 .30 .29
.66 .44
.45 .50 .45
.62 .65 .53
.52 .70 .48
.65 .42 .41
.45 .45 .31
.69 .67
.95 .69
.68 .46
.90 .68
.72 .57
.83 .67
.69 .54
.63
.71
.42
.74
.74
.53
.50
3.—Relationships Between
Indexes Constructed From
Zung SDS in Selected Demographic Subgroups* Age,
Total Men
Zung Well-Belng vs Zung Depressed Mood Zung Somatic Symptoms Zung Optimism Zung Depressed Mood vs Zung Somatic Symptoms Zung Optimism Zung Somatic Symptoms vs Zung Optimism_ 1
Educa- Income, Income,
nth
vs
V406 Easy to do things .62 V408 Hopeful about future .52 V410 Decisions easy .48 V411 Feel useful & needed .50 V412Llfe pretty full .38 V414 Still enjoy things .47 V406 Easy to do things vs V408 Hopeful about future V410 Decisions easy .41 V411 Feel useful & needed .50 V412 Life pretty full .40 V414 Still enjoy things .54 V408 Hopeful about future vs V410 Decisions easy .40 V411 Feel useful & needed .62 V412 Life pretty full .45 V414 Still enjoy things .49 V410 Decisions easy vs .60 V411 Feel useful & needed V412 Life pretty full .50 .44 V414 Still enjoy things V411 Feel useful & needed vs V412 Life pretty full .77 V414 Still enjoy things_.62 V412 Life pretty full vs V414 Still enjoy things_.55
Table
Between Items ¡
Women
Age, >58
yr
yr
Education,
Some
11th Grade
College
Three hundred twenty respondents in selected geographic interviewed with a structured questionnaire that included the Zung Self-Rating Depression Scale. Dimensional analysis indicates that some items are not pure measures of the areas were
constructs they were originally intended to assess. Moreover, some of the dimensions within the scale apparently convey different meanings to different segments in the population. In addition, different dimensions within the scale have varying demographic correlates. The analysis suggests that in order for the scale to be a truly useful device for assessing depressive symptomatology in a general population, additional items need to be added and some questions need to be followed by probes to clarify the exact frame of reference of the respondents.
for understanding any disease is an of the distribution of the illness in the general population and the variables that determine that distribution. In psychiatry such basic information is often lacking. Epidemiological information about the de¬ pressive disorders would be particularly useful since they are not only quite common, but also thought to be influ¬ enced by environmental conditions. Silverman1 has esti¬ mated that the prevalence rate for depressive psychosis is less than one per 1,000 population, and that of depres¬ sive neurosis is two or three times higher. Hordern2 cites higher rates. Others, however, working with special groups, such as nonpsychiatric, medically ill patients, find a very high prevalence of depression.35 The true preva¬ lence of the depressive disorders in the United States is not known.
requirement A understanding basic
Accepted for publication Nov 11, 1974. From the Institute for Social Research,
Arbor.
University of Michigan, Ann
Reprint requests to the Institute for Social Research, University of Michigan, Ann Arbor, MI 48106 (Dr. Blumenthal).
Blum6 has pointed out a major difficulty in studying psy¬ chiatric epidemiology. He states that the method of iden¬ tifying mental illness must have both validity and reli¬ ability. Furthermore, the validity of a diagnosis for which there are no specific laboratory tests or findings depends on the judgment of the clinician, in this case, the psychia¬ trist. Unfortunately, psychiatric diagnosis is characterized by a certain lack of reliability.711 Two of the major studies in psychiatric epidemiology, the Stirling County Study12 and the Midtown Manhattan Study,1' overcame this diffi¬ culty by utilizing psychiatric judgments based on struc¬ tured interviews. By intensively training the psychiatrists who made the disability ratings, the investigators were able to develop procedures that were sufficiently reliable to be satisfactory as research tools. Unfortunately, in choosing this methodology, both studies fail in respect to a third criterion essential to epidemiologie research, that is, that the tool used should be replicable. The device of using extensive training to ensure reliability among the psychi¬ atrists makes it difficult for others to replicate the work. The Zung Self-Rating Depression Scale (SDS) appears to have the validity, reliability, and replicability so impor¬ tant in epidemiological research. It is a 20-item scale mea¬ suring symptoms of depressive illness"15 and has had ex¬ tensive use and considerable validation. The scale is a balanced instrument. Ten of the items are worded so that positive responses indicate the presence of symptomatol¬ ogy. Each item is scored on a four-point scale "a little of the time," "some of the time," "a good part of the time," or "most of the time." Symptom-negative items are scored inversely, and all items are summed to form a total score. It will be shown later that there is some question as to whether or not items that supposedly measure symptoma¬ tology by inquiring about its absence function in the man¬ ner in which they were intended.
Downloaded From: http://archpsyc.jamanetwork.com/ by a La Trobe University User on 07/05/2016
Because the SDS has been extensively used, a consid¬ erable body of evidence has accumulated indicating that the scale has criterion validity, that is, scores on the scale are congruent with what would be expected on the basis of psychiatric diagnosis if the scale were valid. Some of these data are summarized below. Zung first used the scale on 56 psychiatric inpatients who were separated into two groups: those who were both admitted and discharged with the diagnosis of depressive disorder (DD) and those who were admitted as having a depressive disorder but discharged with another diagnosis (DO)." Scores on the SDS of the DD group were higher (mean SDS .73) than those of the DO group (mean SDS .53). (The Zung scale is scored by summing the responses to the items and di¬ viding by 80. For symptom-positive items, "most of the time" equals 4; "a good part of the time" equals 3; "some of the time" equals 2; and "a little of the time" equals 1. The score is then "normalized" according to a table con¬ structed by Zung." Some investigators then multiply the total score by 100.) However, the DO group still scored sig¬ nificantly higher than the normal control subjects who had been psychiatrically screened to rule out individuals with a depressive illness or a history of a recent depressive epi¬ sode (mean SDS .33). Later, Zung et al15 showed that outpatients who were diagnosed as having a psychoneurotic depressive disorder scored significantly higher than pa¬ tients having personality disorders, psychoneurotic anxi¬ ety reactions, and transient situational disorders of adult life, although all three outpatient groups scored higher than the normal controls of the first study. The scale has been shown to be significantly responsive to antidepressant drug treatment in hospitalized patients by some workers,1618 although others have found the scale insensitive to drug-induced change.19 Crosby20 reported that 80% of the patients with spinal and paraspinal in¬ juries scored over 43 (the top of the normal range accord¬ ing to Zung's original study) on the Zung SDS. Since de¬ pression is a common concomitant of paraplegia, Crosby's study provides some validity for the scale. Jacobs et al21 showed mean scores on the Zung SDS were significatnly higher among 50 patients selected by interns as "crocks" than in a group of patients not given such a label. This finding is of interest, since it is well known that patients with depressive illness may have multiple somatic com¬ plaints without prominent symptoms of depressed affect. Such studies indicate the Zung SDS is a useful tool in pop¬ ulations where psychiatric disorder has not been sus¬ pected. In a study of 73 alcoholic patients in an inpatient setting, patients were found to have a mean SDS index of .64,22 a figure somewhat higher than the mean SDS value Zung obtained for his DO group. Variability of depression scores in this group was considerably greater than among Zung's depressed patients. Both the high scores and the greater variability are what might be expected among al¬ coholic patients if the scale had criterion validity, since al¬ coholism is commonly associated with depressive symp¬ toms, although not all alcoholic patients are depressed. In the same study, patients also showed a significant de¬ crease in SDS scores following treatment. Cross-cultural data on the SDS23 are available for Ja¬ pan, Australia, Czechoslovakia, England, Germany, and =
=
=
Switzerland. These studies show a high degree of com¬ parability to the data available from the United States. Moreover, the correlation coefficient between global rat¬ ings made by physicians of the extent of the depression and the SDS range from .43 to .65 for all countries. Some evidence on the construct validity of the instru¬ ment is available. Zung24 found the SDS to correlate with the Depression scale of the Minnesota Multiphasic Person¬ ality Inventory with an r of .59, with the Hamilton De¬ pression Scale with an r of .56,23 with the Beck Scale with an r of .76, and with the Lubin Scale with an r of .29. In addition, the self-rating scale correlates highly (r .87) with observer ratings on the same dimensions.25 A few studies on the methodological characteristics of the scale have been made. High school students were not able to present themselves as less depressed than they actually were, although they could fake more depressed scores when instructed to do so.26 The scale is free of order ef¬ fects.27 The scale has been criticized as inadequate in its cov¬ erage of the spectrum of depressive symptomatology.28 It has also been criticized for not significantly differ¬ entiating between depressed patients located in a general practice, in day care treatment settings, and on an inpatient psychiatric service.29 It is also true that many of the components of depression are covered by a single item. Nevertheless, the scale has a very considerable valid¬ ity that would be exceedingly difficult to reproduce with¬ out extensive effort. Consequently, the SDS appears to be a good choice for the assessment of depressive symptoma¬ tology in a general population. There is a crucial methodological problem, however, that needs to be answered before the value of this instrument as a tool for a study of depression in a general population can be assessed. It is obvious from the construction of the scale that the instrument is multidimensional. Indeed, Zung designed the instrument to cover the range of symp¬ toms that are seen in depressions. Moreover, the scale had been factor analyzed and found to contain four factors.30·31 Thus, the question arises whether or not the major di¬ mensions in the scale have the same meaning for various population segments. This requirement may not seem ob¬ vious, but it can be illustrated. It is well known that the same language may be used quite differently—depending on the circumstances or the user. For example, "How are you" may be a greeting equivalent to "Hello" if it is used in passing down the hall, or it may be a serious inquiry into well-being if made by a physician of a patient. If a scale is to be used in all segments of a population, the items in the various dimensions within a scale must have the same meaning for all the population segments with which the scale is used. This report addresses itself to this =
question.
METHODS
Population Investigated One hundred sixty married couples were interviewed by profes¬ sional female interviewers in the summer of 1972 in the following locations: Lycoming, Penn; Marshall County, Ind; Louisville and Lexington, Ky; St. Joseph County, Flint, and Hancock, Mich; Day¬ ton and Butler, Ohio; and Logan County, Colo. Since the study was
Downloaded From: http://archpsyc.jamanetwork.com/ by a La Trobe University User on 07/05/2016
1.—Percentage Distribution of Selected Demographic Characteristics Among Study Respondents Table
% Men
Characteristic
(N
=
160)
Women
(N
=
160)
Total
(N
=
320)
Age 18-29 y r 30-39 yr 40-49 yr 50-59 yr
>60yr Total Race Black White Total Income
29 20 14 15
35 18 13 18
22 100
100
96 100
>$6,000 $6,000-89,999 $10,000-12,499 $12,500-$14,999 >$15,000
23 29 22 10
Total
Occupational status Currently employed Retired Laid off or unemployed Housewife Student or other Total Marital status First marriage Marriage after divorce Marriage after death of
32 19 13 16 20 100
100 74 20
29
51 11
65
32
100
100
100
85 13
83 15
84
100
100
100
11
15 16 39 15 15 100
14
previous spouse Total Education 0-8 yr 9-11 yr High school graduate Some college
16 31 16
>4yr college Total
100
48 13 12 100
meant to be primarily methodological, the sample was not de¬ signed to represent the US population or any specific region. The interviewers were assigned 10 to 20 segments (a segment is a des¬ ignated area with specified geographic boundaries containing 20 to 30 addresses within one of the Survey Research Center's pri¬ mary sampling units), given a specific geographic location marked on a map as a starting point, and instructed to proceed around each segment in a clockwise direction. The interviewers made at every third household unit until the as¬ of couples had been interviewed. If the required number of interviews could not be obtained in the first trip around the segment, the interviewer started again at the beginning of the segment, traveling in the same direction but beginning with the second house. Interviewers were required to interview from two to three couples for each two segments, depending on the size of the segment. The interviewers worked in pairs, and interviews of the couples were conducted simultaneously with the two spouses. Interviews were held in separate rooms whenever pos¬ sible (about 95% of the cases). A total of 320 married people were interviewed. The interview was a structured instrument that the inter-
requests for interviews
signed number
viewers were required to follow exactly. The interview, which lasted approximately an hour, centered mainly on the respon¬ dent's work, his marriage, and his social relationships. The inter¬ viewers recorded the answers given them and made nondirective probes. They did not rate the respondents in any way. Coding was conducted according to methods standard at the Survey Research Center.32 Table 1 shows the characteristics of the respondent
population. RESULTS
The responses to the items in the Zung SDS were inter¬ related using gammas, which are a measure of association suitable for ordinal data.33 The gamma matrix was then subjected to a Guttman-Lingoes Smallest Space Analy¬ sis.34·35 The analysis yielded three main clusters in three dimensions with a coefficient of alienation of .14 and a Kruskal stress coefficient of .12. The items within each di¬ mension were subjected to additional analysis to deter¬ mine if the relationships between items within a cluster were similar for a variety of subgroups within the popu¬ lation. The basic principle of the dimensional analysis was that items within a dimension or cluster should show consist¬ ent interitem relationships within selected demographic subgroups. If such relationships are reasonably consistent, one can assume that the items are viewed similarly by those subgroups and probably most people in the popu¬ lation. If relationships are inconsistent, the meaning of the items probably varies from group to group. This anal¬ ysis strategy for survey data is outlined in Blumenthal et al.36 The subgroups chosen as units of replication are shown in Table 2, which illustrates this type of analysis. The Table shows all the interitem correlations for those items that were contained in the largest cluster suggested by the Smallest Space Analysis, the Zung Well-Being Cluster. This cluster consists of seven of the ten positively worded items in the Zung scale: mind is as clear as it used to be find it easy to do the things I used to feel hopeful about the future find it easy to make decisions feel that I am useful and needed My life is pretty full I still enjoy the things I used to
My I I I I
Interestingly enough, these same seven items were found on the first factor in the factor analysis of data by Rickels et al30 from 831 depressed outpatients. These items are designed to be the reverse of items indicating depres¬ sive symptoms. However, their face value indicates a state of well-being. The fact that statements that are as diverse in content as the equivalent of psychomotor retardation ("I find it easy to do the things I used to") are in the same cluster with the putative equivalent of confusion ("My mind is as clear as it used to be") and hopelessness ("I feel hopeful about the future") underlines the possibility that the respondent may be reacting to the positive element in the items rather than to the specific symptom (or lack of to load
it) that the item is supposed to represent. Inspection of Table 2 shows a number of low correla¬ tions between items (gammas below .4), particularly
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Table
2.—Relationships All Re¬ spon¬
dents
(N) V405 Mind clear
(320) as
usual
Confi¬ dence
Zung Well-Belng Clusters for Selected Subgroups (Gammas)
Worn-
Age,
Age,
58
Educa-
Some
Previ-
tion,
College
ously
Men
en
yr
yr
Grade
(160)
(160)
(69)
(72)
(98)
(96)
.49-.75 .39-.65 .34-,62 .36-.64 .23-.53 -33-.61
.63 .59 .52 .54 .37 .52
.61 .47 .44 .46 .40 .42
.74 .63 .41 .61 .52 .53
.34 .57 .42 .29 .26 .23
.66 .51 .42 .55 .32 .55
.74 .70 .45 .53 .48 .66
.50 .42 .37 .33 .33 .44
.67 .62 .61 .56 .55 .49
,33-.59 .28-.54 .36-,64 .25-.55 .40-.68
.44 .39 .45 .37 .51
.49 .44 .54 .41 .57
.71 .45 .60 .53 .65
.16 .31 .37 .38 .35
.38 .34 .45 .48 .57
.79 .44 .64 .57 .60
.19 .36 .50 .38
.26-.S4 .43-.76 .30-.60 .35-.63
.36 .60 .38 .36
.43 .65 .50 .59
.43 .84 .69 .52
.09 .33 .24 .12
.31 .64 .45 .60
.54 .71 .66 .62
.46-.74 .35-. 5 .30-.58
.52 .56 .44
.69 .45 .43
.69 .38 .35
.47 .58 .26
.53 .49 .53
.74
.63-.91 ,48-.76
.76 .67
.77 .60
.90 .64
.63 .53
.40-.70
.58
.53
.54
.42
tion
Di-
$12,500 vorced (80) (44) (69)
Interval
Married Married >5 yr >21 yr
(90)
(136)
.56 .33 .35 .56 .17 .28
.75 .52 .28 .48 .36 .54
.44 .47 .51 .33 .21 .31
.64 .64 .55 .55 .61
.31 .40 .55 .38 .50
.63 .37 .55 .41 .66
.25 .39 .37 .35 .43
.08 .45 .13 .21
.64 .71 .68 .64
.62 .69 .65 .56
.47 .82 .54 .56
.16 .44 .30 .29
.66 .44
.45 .50 .45
.62 .65 .53
.52 .70 .48
.65 .42 .41
.45 .45 .31
.69 .67
.95 .69
.68 .46
.90 .68
.72 .57
.83 .67
.69 .54
.63
.71
.42
.74
.74
.53
.50
3.—Relationships Between
Indexes Constructed From
Zung SDS in Selected Demographic Subgroups* Age,
Total Men
Zung Well-Belng vs Zung Depressed Mood Zung Somatic Symptoms Zung Optimism Zung Depressed Mood vs Zung Somatic Symptoms Zung Optimism Zung Somatic Symptoms vs Zung Optimism_ 1
Educa- Income, Income,
nth
vs
V406 Easy to do things .62 V408 Hopeful about future .52 V410 Decisions easy .48 V411 Feel useful & needed .50 V412Llfe pretty full .38 V414 Still enjoy things .47 V406 Easy to do things vs V408 Hopeful about future V410 Decisions easy .41 V411 Feel useful & needed .50 V412 Life pretty full .40 V414 Still enjoy things .54 V408 Hopeful about future vs V410 Decisions easy .40 V411 Feel useful & needed .62 V412 Life pretty full .45 V414 Still enjoy things .49 V410 Decisions easy vs .60 V411 Feel useful & needed V412 Life pretty full .50 .44 V414 Still enjoy things V411 Feel useful & needed vs V412 Life pretty full .77 V414 Still enjoy things_.62 V412 Life pretty full vs V414 Still enjoy things_.55
Table
Between Items ¡
Women
Age, >58
yr
yr
Education,
Some
11th Grade
College
