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An Investigation of Female Adolescent Twins With Both Major Depression and Conduct Disorder
An Investigation of Female Adolescent Twins With Both Major Depression and Conduct Disorder NAOMI R. MARMORSTEIN, B.A., AND WILLIAM G. IACONO, PH.D.
ABSTRACT Objective: Conduct disorder (CD) and major depression (MDD) frequently co-occur in adolescents, but little is known about the characteristics and functioning of youths, especially females, with both disorders. This study describes the functioning of female adolescents with histories of both CD and MDD. Method: Subjects were selected from an epidemiological sample of 17-year-old female twins based on having a lifetime DSM-III-R diagnosis of MDD and/or CD; control subjects had no history of either disorder. Results: In nearly all domains examined, including measures of academic success (including academic achievement and school adjustment), personality, quality of peer relationships, and high-risk behavior (including substance dependence and early sexual experience), main effects of one or both disorders were found and related to impaired functioning. In addition, interaction effects were found in the areas of substance dependence symptoms (for all classes of substances), negative school-related events, and a personality-based predisposition not to experience positive emotions, indicating that those with both diagnoses were especially impaired. Conclusions: In some domains, histories of MDD and CD interact and relate to particularly severe problems. The implications of these findings for research and treatment, including the high likelihood of substance and school adjustment problems in these youths, are discussed. J. Am. Acad. Child
Adolesc. Psychiatry, 2001, 40(3):299–306. Key Words: conduct disorder, depression, comorbidity, adolescents, females.
Adolescents with either major depression (MDD) or conduct disorder (CD) are at risk for a variety of negative outcomes, both during adolescence and into adulthood, in domains such as academic achievement (e.g., Bardone et al., 1996; Hodges and Plow, 1990), peer relationships (e.g., Cole and Carpentieri, 1990; Renouf et al., 1997), and substance abuse (e.g., Greenbaum et al., 1991; Whitmore et al., 1997). Complicating the effort to understand each of these disorders is the fact that MDD and CD (as well as the more broad domains of depressive symptoms and conduct problems) are often correlated. That is, individuals frequently exhibit both depression and conduct problems, a fact that is striking because many consider these two disorders to represent distinct types of Accepted October 17, 2000. From the Department of Psychology, University of Minnesota, Minneapolis. This study was supported by grants DA05147 from the National Institute on Drug Abuse and AA09367 from the National Institute on Alcohol Abuse and Alcoholism. The authors thank Matt McGue, Ph.D., for his work on the Minnesota Twin Family Study and his comments on an earlier draft of this paper. Reprint requests to Dr. Iacono, Department of Psychology, University of Minnesota, 75 East River Road, Minneapolis, MN 55455. 0890-8567/01/4003-0299䉷2001 by the American Academy of Child and Adolescent Psychiatry.
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behavior—internalizing (depression) and externalizing (CD). Approximately 15% to 25% of youths with CD have comorbid MDD; approximately 15% to 35% of depressed youths exhibit comorbid CD (see review by McCracken et al., 1993). Adolescents with both depression and conduct problems may be at even greater risk for substance dependence (e.g., Riggs et al., 1995) and treatment-seeking (Rohde et al., 1991; Sack et al., 1993) than youths with only one of these problems. They may have lower IQ scores than those with an affective disorder only (Noam et al., 1994), as well as more academic problems than those with disruptive behavior only (Lewinsohn et al., 1995). Poor social competence (Renouf et al., 1997) and maladaptive peer relationships (Asarnow, 1988; Cole and Carpentieri, 1990) are also associated with the co-occurrence of depression and CD. It remains unclear whether the presence of these two disorders together relates to an earlier initiation of sexual activity than one of these disorders alone. Unfortunately, youths with both types of problems may be less amenable to traditional treatments than youths with only one of these disorders (Hughes et al., 1990). Longitudinally, youths with both conduct problems and depression are prone to increased long-term 299
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problems in functioning (including adult criminality), compared with depressed-only youths (Capaldi, 1992; Harrington et al., 1991; Kovacs et al., 1988). Although personality is not a domain of functioning per se, it represents another aspect of an adolescent that likely relates to his or her well-being. It is reasonable to expect that certain aspects of personality would be associated with different types of psychopathology, and studies of late adolescents with affective disorders and CD have confirmed that their personality profiles differ from those of people without these disorders (Krueger et al., 1996; Trull and Sher, 1994). However, far fewer personality differences between disordered and nondisordered individuals emerge when those who have comorbid conditions are excluded (Krueger et al., 1996). The profiles of subjects with the specific pattern of comorbidity evident in this study have not been examined. Females with both depression and conduct problems represent a group that is in particular need of attention. There is indirect evidence that internalizing and externalizing problems may be linked more strongly in females than in males (e.g., Robins, 1986), although the findings to date are far from clear. There is also research describing differences in the problems associated with these disorders in females and males. For example, the relationship among substance abuse, depression, and conduct problems appears to differ for females and males (Bukstein et al., 1992; Clark et al., 1997; Hovens et al., 1994; King et al., 1996; Whitmore et al., 1997), although there is inconsistency in findings regarding the specifics of these differences. Adding to the ambiguity regarding potential gender differences is the fact that many studies (particularly those on CD) include only male subjects. This is the case despite evidence that CD does, in fact, occur in females and does relate to substantial problems in adulthood for those females who are affected by it (e.g., Bardone et al., 1996, 1998). Knowledge about youths with both disorders has significant implications for the existing bodies of literature on depression and conduct problems in adolescents. Studies that examine one of these disorders generally either exclude subjects with additional disorders or ignore potential co-occurring conditions. If subjects with both disorders are indeed different from those with only one in ways that are relevant to the topic under study, results of both types of studies would be problematic. Studies that exclude people with both conditions may be studying an atypical sample. However, if potential co-occurring conditions are simply ignored, the findings may be due to only 300
a subset of subjects (e.g., those who have additional psychological disorders) who are particularly extreme in some way. Thus it is important to elucidate the similarities and differences between people with single conditions and those with co-occurring conditions, especially when two disorders are highly correlated. This study attempted to reduce this gap in research by examining functioning and personality factors in female youths with histories of both depression and CD. In particular, potential interactions between depression and CD were examined, to determine whether youths with both disorders were simply experiencing direct effects of each disorder or whether the interaction of the two disorders was particularly detrimental. METHOD Subjects Subjects were assessed as part of the Minnesota Twin Family Study (MTFS), an epidemiological study of twins and their parents. The MTFS uses a population-based twin ascertainment method in which all female twins who were born in the state of Minnesota during specified years were identified from public birth records. Of these identified families who were eligible, 17.3% refused to participate. There were no significant occupational differences between parents of families who participated and those who declined. After excluding twins who were not suitable candidates for the study (for example, the adolescents were mentally retarded or adopted), the final sample included 337 families of female twins from around the state. The twins were recruited to be approximately age 17 at the time of the family’s visit to the study. For details regarding the design of this epidemiological study, see Iacono et al. (1999). Affected subjects were selected on the basis of having a lifetime diagnosis of MDD and/or CD at either the definite (meeting all DSM-III-R [American Psychiatric Association, 1987] criteria for the disorder) or probable (exhibiting all except one symptom for a DSM-III-R diagnosis) level. A diagnosis was considered present if either the subject herself or her mother reported that the adolescent had experienced enough symptoms. To assess symptoms of MDD, the Structured Clinical Interview for DSM-III-R (SCID) (Spitzer, 1990; Spitzer et al., 1987) was administered to adolescents and a modified version of the Diagnostic Interview for Children and Adolescents-Parent version (DICA-P) (Reich and Welner, 1988) was administered to mothers. To assess symptoms of CD, an MTFS interview that assesses DSM-III-R symptoms of CD was conducted with the adolescents and the DICA-P was administered to mothers. Interviewers had bachelor’s or master’s degrees in psychology or related fields and received intensive training in diagnostic interviewing. The diagnostic interviews were reviewed by teams of advanced clinical psychology doctoral students, who coded the presence or absence of symptoms on the basis of written notes and audiotapes of the interviews. Kappa reliabilities for these diagnoses were as follows: SCID MDD, κ = 0.89; DICA-P MDD, κ = 0.91; MTFS interview CD, κ = 0.85; and DICA-P CD, κ = 0.75. When this method of subject selection was used, approximately 13% (87) of the entire sample met criteria for MDD but not CD, 7% (46) met criteria for CD but not MDD, and 3% (21) meet criteria for both disorders. Thus 31% of subjects with a history of CD
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also had a history of MDD, and 19% of those with a history of MDD also had a history of CD. In no case were two subjects from the same family included in the study. When both twins in a family were affected by a disorder, the subject with the more severe case (more symptoms or symptoms reported by both the mother and the adolescent) was included. When one twin was affected by one disorder and the other twin was affected by both disorders, the twin with both disorders was included. MDD-only subjects who had two or more symptoms of significant antisocial behavior after the age of 15 were excluded. When one twin had CD only while the other had MDD only, both twins were excluded. Control subjects were selected by identifying all families in which neither twin had symptoms of either target disorder, then randomly selecting one adolescent from each of these families. This resulted in the final inclusion of 25 subjects with only CD, 53 subjects with only MDD, 20 subjects with both CD and MDD, and 126 control subjects. Of the 73 subjects with lifetime histories of MDD, 11 (15%) were depressed at the time of the assessment. Ninety-seven percent of the subjects were white, reflecting the demographic makeup of Minnesota at the time they were born (there were no significant group differences on this variable; χ23 = 1.39, p > .05). CD-only subjects were slightly older than CD+MDD subjects at the time of their assessment (mean = 17.7 years for CD-only subjects, compared with 17.3 years for CD+MDD subjects; F3,223 = 3.97, p < .01). Parents’ ages did not differ across groups (F3,435 = 1.94, p > .05). Parental socioeconomic status, as measured by the Hollingshead Four Factor Index of Social Status (Hollingshead, 1975), did not differ across groups (F3,470 = 0.65, p > .05). The average Hollingshead score (4.02) corresponded to occupations such as clerical and sales workers, technicians, and small-business owners. Measures Academic Success. Four subtests of the WAIS-R (Wechsler, 1981) (Vocabulary, Block Design, Picture Arrangement, and Similarities) were administered. Scores were prorated to estimate subjects’ Full Scale IQs. Raw scores on the Wide Range Achievement Test-Revised (Jastak and Wilkinson, 1984) were used as a standardized measure of academic achievement. Adolescents’ reports of overall grade point average (GPA), collected during their interviews, were used as an estimate of grades earned. A composite of negative school-related events (failing classes and getting suspended or expelled) was used as a measure of school adjustment problems. Personality. A modified version of the Multidimensional Personality Questionnaire (A. Tellegen, unpublished, 1982), a self-report personality inventory, was used to assess various aspects of subjects’ personalities. This is a 198-item questionnaire with a 4-point “definitely true” to “definitely false” response format. It assesses 11 primary personality traits (Well-Being, Social Potency, Achievement, Social Closeness, Stress Reaction, Alienation, Aggression, Control, Harm Avoidance, Traditionalism, and Absorption) and yields scores on 3 higher-order factors: Positive Emotionality, or the predisposition to experiencing positive affect (Well-Being, Social Potency, Achievement, and Social Closeness); Negative Emotionality, or the predisposition to experiencing negative affect (Stress Reaction, Alienation, and Aggression); and Constraint, or a measure of behavioral constraint (Control, Harm Avoidance, and Traditionalism). Peer Relationships. Peer relationships were assessed with an MTFS computerized questionnaire that requires that subjects respond to a variety of statements about their peer group by indicating whether “All my friends are like that,” “Most of my friends are like that,” “Just a few of my friends are like that,” or “None of my friends are like that.” Subjects with high scores on the measure of positive peer models tend
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to have friends who work hard to get good grades in school, do their homework and study a lot, are very smart, get good grades in school, and are liked by their teachers, whereas those with high scores on the measure of negative peer models tend to have friends who break rules, drink alcohol, smoke cigarettes or chew tobacco, steal things from others, use drugs, know where to buy drugs, and get into trouble with the police. Alpha reliabilities of each scale were adequate (.78 for positive peer models and .85 for negative peer models). High-Risk Behavior. DSM-III-R substance use disorder symptoms and diagnoses were assigned on the basis of the adolescents’ reports on a modified version of the Substance Abuse Module (Robins et al., 1987, 1988), a supplement to the World Health Organization’s Composite International Diagnostic Interview (Robins et al., 1988). Both counts of the number of dependence symptoms present for each class of substance (nicotine, alcohol and drugs) and actual substance abuse and dependence diagnoses were used in analyses. For the drug dependence symptom count, all symptoms of dependence across all types of drugs were summed (for example, an adolescent with one symptom of cannabis dependence and two symptoms of amphetamine dependence would be assigned a symptom count of three). Substance diagnoses were assigned according to the same procedure outlined above for MDD and CD (under “Subjects”). Substance dependence diagnoses were considered present if the DSM-III-R diagnostic requirements were met at either the definite or probable (missing one symptom) level. Substance abuse diagnoses were assigned only if all diagnostic criteria were met (because only one clinical symptom, plus a duration requirement, is required for these diagnoses). Abuse and dependence diagnoses were combined to create a single substance use disorder variable for each class of substance (nicotine, alcohol, and drugs). Reliabilities of substance use disorder diagnoses exceeded κ = 0.90. During an interview assessing the occurrence and timing of various life events, subjects were asked whether or not they had ever had consensual sexual intercourse. If they responded yes, they were asked the age at which they first did so. Statistical Analyses Two-factor analyses of variance (ANOVAs) were conducted (presence/absence of MDD diagnosis ⫻ presence/absence of CD diagnosis) for all continuous dependent variables to assess for main effects of each disorder and interaction effects. For dichotomous dependent variables (presence or absence of substance use diagnoses and whether or not subjects had initiated sexual activity by the time of their age 17 assessment), logit analyses were conducted to investigate the relationship between MDD diagnosis (present/absent), CD diagnosis (present/ absent), and MDD ⫻ CD interactions and the dependent variable. A separate logit analysis was conducted for each dependent variable; first, a model without interaction effects was compared with the saturated model to determine the importance of the interaction to predicting the dependent variable. Next, models without main effects for each diagnosis were examined to determine the importance of each diagnosis in predicting the dependent variable. RESULTS
The results of all analyses are summarized in Table 1 and Figure 1. Academic Success
No significant main or interaction effects were found in the prediction of subjects’ Full Scale IQ scores or on a 301
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A
B
standardized test of academic achievement. There was a main effect of CD on the prediction of overall GPA. This CD main effect was reflected in the lower GPAs of both CD groups relative to controls, but only the CD+MDD mean GPA was significantly lower in post hoc tests. This pattern, in which a diagnostic main effect is significant but at most one post hoc test involving subgroups differs significantly from controls, appears in several subsequent analyses and illustrates the additional power afforded by ANOVA to detect effects. In addition, there were main effects of both MDD and CD, and an interaction effect of the two disorders, on the prediction of a composite of negative school-related events. Thus it appears that CD alone is related to relatively poor grades, and while each diagnosis is independently associated with increased numbers of negative school-related events, the interaction of both disorders together relates to a particularly high rate of these events. Personality
C
Multidimensional Personality Questionnaire results indicated that main effects for both MDD and CD were present when predicting subjects’ predispositions to experiencing negative emotions and levels of behavioral constraint. When predicting subjects’ predispositions to experiencing positive emotions, we found a main effect for MDD; in addition, an MDD ⫻ CD interaction effect was found. Thus both MDD and CD are related to a predisposition to experience negative emotions and are associated with low levels of behavioral constraint. In addition, MDD is associated with a low level of positive emotionality; MDD and CD also interact in this area and together are associated with a particularly strong predisposition not to experience positive emotions. Peer Relationships
Fig. 1 Number of symptoms of nicotine, alcohol, and illicit drug dependence as a function of the presence or absence of conduct disorder (CD) and major depression (MDD). Because these three symptom count variables were skewed, each was log-transformed (one was added to each subject’s score and the base 10 log was taken) and analyses were repeated. The results were the same as those presented. 䊉 = MDD absent; 䊊 = MDD present.
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Main effects for both MDD and CD were found in the prediction of relatively high levels of negative peer models. In contrast, only a main effect of CD was found in the prediction of low levels of positive peer models. Thus both MDD and CD are independently related to having large numbers of friends who engage in antisocial behavior, while only CD is related to having few friends who engage in prosocial behavior. High-Risk Behavior
When the percentages of subjects with substance use disorder diagnoses (substance abuse or dependence) were J . A M . A C A D . C H I L D A D O L E S C . P S YC H I AT RY, 4 0 : 3 , M A RC H 2 0 0 1
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TABLE 1 Means (and Percentages With Dichotomous Outcomes) for All Diagnostic Groups and ANOVA F Values/Logit Analysis χ2 Values Means (SDs) (and Percentage With Outcomes) for Groups With Psychopathology and Controls a Domain Academic success IQ (Full Scale): mean (SD) WRAT-R (raw score): mean (SD) GPA (overall): mean (SD) No. of negative school eventsc: mean (SD) Personalityd Negative emotionality: mean (SD) Positive emotionality: mean (SD) Constraint: mean (SD) Peer relationshipsd Positive peer models: mean (SD) Negative peer models: mean (SD) High-risk behavior (%) Nicotine dependence Alcohol diagnosis Drug diagnosis Sexual activity by 17
CD + MDD (n = 17–20)
CD Only (n = 21–25)
MDD Only (n = 41–53)
Controls (n = 109–126)
100.20 (11.04) 58.25 (9.52) 2.68a (0.89) 1.25ab (0.79)
94.92 (12.20) 53.64 (9.42) 3.00 (0.87) 0.65ab (0.78)
97.89 (11.00) 59.54 (8.76) 3.15 (0.64) 0.22b (0.47)
97.45 (15.54) 58.07 (9.87) 3.27a (0.69) 0.10a (0.31)
60.30a (12.28) 43.33 (14.27) 34.93ab (13.06)
55.52 (9.71) 50.88 (7.33) 43.44 (13.67)
54.90b (11.14) 50.06 (10.30) 47.41b (10.78)
43.30 (15.90) 66.70 ac (13.92)
43.30 (7.34) 60.95b (11.16)
65.00 ac 60.00 ab 40.00 a 85.00 a
40.00bd 28.00ac 20.00b 64.00b
F/χ2b MDD
CD
MDD ⫻ CD
0.23
0.96
0.31
3.46
3.06
0.93
2.92
8.56**
0.62
18.01***
87.30***
8.10**
50.00ab (10.00) 50.00 (10.00) 50.00a (10.00)
6.43*
8.15**
0.00
4.01*
2.44
4.13*
7.75**
22.82***
2.21
50.55 (11.19) 53.81c (9.12)
50.00 (10.00) 50.00ab (10.00)
0.02
12.49**
0.89
6.21*
38.59***
0.26
13.21cd 9.43bc 7.55a 45.28a
5.56ab 2.38a 0.00ab 21.43ab
5.80* 9.00** 8.98** 12.92***
44.35*** 42.91*** 34.28*** 27.86***
0.01 0.01 2.91 0.00
Note: ANOVA = analysis of variance; CD = conduct disorder; MDD = major depression; WRAT-R = Wide Range Achievement Test-Revised; GPA = grade point average. a Groups with the same subscript are significantly different from each other (p < .05, based on post hoc multiple comparison tests using the Bonferroni correction). b Continuous variables (those with means and SDs) were analyzed with two-factor ANOVAs, with resulting F values reported. Categorical variables (those expressed as percentages) were evaluated with logit analyses, with resulting χ2 values reported. c Because this variable was skewed, a log-transformation was done (1 was added to each subject’s score, then the base 10 log was taken) and the analysis was repeated. The results were identical with those presented above. d Values are T scores derived from the control participants who had a mean of 50 and SD of 10. * p < .05; ** p < .01; *** p < .001.
examined with logit analyses, main effects for MDD and CD were found for all classes of substances (nicotine, alcohol, and drugs). Although no interaction effects were statistically significant, for drug use disorders the interaction of MDD and CD approached significance (p < .09), and for all three disorders the CD+MDD group had an elevated rate of disorder. When the number of symptoms of substance dependence was examined, for all three classes of substances the main effects for MDD (all F1,222 values > 14.15, all p values < .001) and CD (all F1,222 values > 43.25, all p values < .001) were significant. In addition, the three J . A M . A C A D . C H I L D A D O L E S C . P S YC H I AT RY, 4 0 : 3 , M A RC H 2 0 0 1
MDD ⫻ CD interaction effects (all F1,222 values > 12.50, all p values < .001) were significant. The average number of substance dependence symptoms (for each class of substance) reported by subjects with each combination of diagnoses is presented in Figure 1. For each class of substance, all subjects without CD evidenced relatively low numbers of symptoms. However, in the presence of CD, the number of dependence symptoms was highly related to the presence or absence of MDD. Main effects of MDD and CD were found to relate to whether subjects reported having had sexual intercourse by the time of their assessments at age 17. In addition, among 303
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those subjects who had engaged in sexual activity (n = 84), both MDD and CD exerted main effects on the age at first intercourse (F1,81 = 6.06, p < .05 for MDD; F1,81 = 22.91, p < .001 for CD). No interaction of MDD and CD was found (F1,81 = 0.64, p > .05). Among subjects who reported having had sex, those with histories of both disorders initiated sexual activity at age 14.76 (SD = 1.20), whereas those with only CD initiated at 15.44 (SD = 1.03), those with only MDD initiated at 15.92 (SD = 0.93), and those with neither disorder initiated at 16.26 (SD = 0.59). Thus both MDD and CD are associated with sexual activity by age 17, and among subjects having engaged in sexual activity by age 17, both disorders are associated with sexual activity at particularly young ages. Effects of Acute Depression
Because it was possible to determine which subjects were depressed at the time of their assessment, acutely depressed participants (n = 11) were excluded and all analyses were repeated. The results did not change appreciably. In two instances, findings that had been statistically significant were reduced to trends (MDD main effects for positive and negative emotionality; p values < .10). One additional main effect for MDD was found (score on the Wide Range Achievement Test-Revised; F1,212 = 4.40, p < .05). DISCUSSION
The results of this study suggest that both depression and CD are related to significant difficulties in functioning, as well as particular personality characteristics, for female adolescents. Because depression and CD frequently have detrimental main effects on the same areas of functioning, these disorders sometimes interact to produce especially poor outcomes. This is particularly the case with respect to substance dependence: the combination of these two disorders is associated with particularly high numbers of symptoms (more than would be expected considering only the effects of each disorder alone). Although a similar trend was seen for substance disorder diagnoses, the interaction effect was not significant. The difference in the outcome of these two analyses may derive from the increased power to detect an interaction effect in the analysis if continuous, as opposed to categorical, data are used. Depression and CD also interact in relation to school adjustment and the personality dimension of positive emotionality. Each disorder alone is related to increased numbers of negative school-related events such as sus304
pension and failure of classes; together, these disorders are related to even more problems of this sort than would be expected on the basis of only the main effects of each disorder. This is consistent with previous research indicating that depression and disruptive behavior together are related to more school problems than disruptive behavior alone (Lewinsohn et al., 1995). Both disorders together are also associated with a lowered predisposition to the experience of positive emotions, even though when the disorders are considered separately only depression is related to low scores on this dimension. In other domains, however, depression and CD relate to difficulties in functioning but do not interact to produce impairments beyond what would be expected if one were considering the presence or absence of each disorder separately. When considering certain dimensions of personality (negative emotionality and behavioral constraint), peer relationships (the predominance of negative peer models), and high-risk behavior (early sexual behavior), both depression and CD exert main effects that relate to problems in these areas. Thus, previous studies’ findings that youths with both disorders have maladaptive peer relationships (Asarnow, 1988; Cole and Carpentieri, 1990) may simply be due to the presence of each disorder independently and not to any interaction between the disorders. In contrast, overall GPA and the presence of few positive peer models are uniquely associated with the effects of CD. Depression is uniquely associated with low levels of positive emotionality (as discussed above, depression and CD also interact in this area). This study’s analysis of a group of females with conduct problems (both with and without depression) is relatively rare; therefore, several aspects of the findings merit brief discussion. First, the domains in which depression and CD are associated with problems in functioning for females are similar to those that would likely be found in males with these disorders; that is, they are similar to those found in males with conduct problems, with or without comorbid conditions. Second, although both disorders are related to impaired functioning in a variety of domains, when substance use problems are examined the interaction of these disorders is associated with a level of pathology that is quite striking. The relationship among depression, conduct problems, and substance use problems in females raises cause for serious concern and therefore merits further study, particularly because there may be gender differences in this relationship (e.g., Clark et al., 1997; Whitmore et al., 1997) that J . A M . A C A D . C H I L D A D O L E S C . P S YC H I AT RY, 4 0 : 3 , M A RC H 2 0 0 1
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render findings based on samples of males not applicable to females. The findings of this study have implications for research focused on one or the other of these disorders. With approximately one fifth of those with a history of depression also having a history of CD and approximately one third of those with CD also having a history of depression, substantial numbers of youths apt to be included in studies of each single disorder likely have the other disorder. It is important that, whenever possible, researchers either study “pure” groups (i.e., without co-occurring conditions, resulting in an unrepresentative sample of those with the disorder) or carefully incorporate the other disorder into the research design. Because these disorders frequently relate to impairments in the same domains (and sometimes interact as well), studies that simply ignore potentially co-occurring disorders may therefore obscure the true effects of either disorder. Limitations
Several limitations of this study should be noted. First, it should be remembered that subjects in this study were selected from an epidemiological sample of adolescents. Therefore, cases of CD and depression may have been less severe and/or impairing than cases of these disorders found in clinic settings. It is, however, striking that despite the nonclinical nature of this sample, subjects in this study evidenced significantly impaired functioning in a variety of domains. In addition, subjects in this study had histories of these disorders; they did not necessarily have active symptoms at the time of assessment, nor did they necessarily have both disorders at the same time. Subjects also may have had other psychiatric disorders; because of the population-based nature of this sample, those other disorders represent what would naturally occur in adolescents with these disorders. It is also possible that some of the nonsignificant findings associated with the smaller diagnostic groups can be attributed to these groups having relatively fewer subjects. It is crucial to note that this study did not address the issue of causality. Thus it is not known whether the disorders caused the functional problems, the functional problems precipitated the development of the disorders, or some third factor (e.g., temperament) underlies both the disorders and the functional problems. Finally, subjects in this study were primarily white. Although this reflects the demographic makeup of Minnesota at the time they were born, it may limit the applicability of the findings to other groups. J . A M . A C A D . C H I L D A D O L E S C . P S YC H I AT RY, 4 0 : 3 , M A RC H 2 0 0 1
Clinical Implications
It is apparent that youths presenting with either disorder need to be carefully assessed for the other disorder. For those youths found to have both disorders, thoughtful treatment of both problems, regardless of which is the presenting problem, will likely be necessary. Currently, clinicians must rely on treatments developed for youths with only one of these two disorders, although these may be less effective in treating people with both disorders (e.g., Hughes et al.,1990). Fortunately, there is some indication that successfully treating one disorder may result in improvements in the other (Puig-Antich, 1982). Clinicians must be aware that the course of the “primary” disorder may be altered by the presence of the other disorder. For example, it has been suggested that the outcomes of depressed children with CD closely resemble those of nondepressed children with CD (and do not as closely resemble those of depressed children without CD) (Harrington et al., 1991). It must be remembered that substance use problems are the norm, not the exception, in this group. Interventions aimed at changing the peer groups of these youths, their school-related behavior, and their patterns of substance use will be appropriate for many clients. Behavior changes in these areas will likely complement the treatment of the psychopathology and prevent other potential associated problems (e.g., sexually transmitted diseases, school dropout). In addition, identifying youths with one disorder who are particularly at risk for developing the other disorder could aid in prevention efforts. More information about the potentially unique etiology of the co-occurrence of depression and CD would also aid in the development of effective prevention and treatment strategies. REFERENCES American Psychiatric Association (1987), Diagnostic and Statistical Manual of Mental Disorders, 3rd edition-revised (DSM-III-R). Washington, DC: American Psychiatric Association Asarnow JR (1988), Peer status and social competence in child psychiatric inpatients: a comparison of children with depressive, externalizing, and concurrent depressive and externalizing disorders. J Abnorm Child Psychol 16:151–162 Bardone AM, Moffitt TE, Caspi A, Dickson N, Silva PA (1996), Adult mental health and social outcomes of adolescent girls with depression and conduct disorder. Dev Psychopathol 8:811–829 Bardone AM, Moffitt TE, Caspi A, Dickson N, Stanton WR, Silva PA (1998), Adult physical health outcomes of adolescent girls with conduct disorder, depression, and anxiety. J Am Acad Child Adolesc Psychiatry 37:594–601 Bukstein OG, Glancy LJ, Kaminer Y (1992), Patterns of affective comorbidity in a clinical population of dually diagnosed adolescent substance abusers. J Am Acad Child Adolesc Psychiatry 31:1041–1045
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Capaldi DM (1992), Co-occurrence of conduct problems and depressive symptoms in early adolescent boys, II: a 2-year follow-up at grade 8. Dev Psychopathol 4:125–144 Clark DB, Pollock N, Bukstein OG, Mezzich AC, Bromberger JT, Donovan JE (1997), Gender and comorbid psychopathology in adolescents with alcohol dependence. J Am Acad Child Adolesc Psychiatry 36:1195–1203 Cole DA, Carpentieri S (1990), Social status and the comorbidity of child depression and conduct disorder. J Consult Clin Psychol 58:748–757 Greenbaum PE, Prange ME, Friedman RM, Silver SE (1991), Substance abuse prevalence and comorbidity with other psychiatric disorders among adolescents with severe emotional disturbances. J Am Acad Child Adolesc Psychiatry 30:575–583 Harrington R, Fudge H, Rutter M, Pickles A, Hill J (1991), Adult outcomes of childhood and adolescent depression, II: links with antisocial disorders. J Am Acad Child Adolesc Psychiatry 30:434–439 Hodges K, Plow J (1990), Intellectual ability and achievement in psychiatrically hospitalized children with conduct, anxiety, and affective disorders. J Consult Clin Psychol 58:589–595 Hollingshead AB (1975), Four Factor Index of Social Status. New Haven, CT: Yale University Department of Sociology Hovens JGFM, Cantwell DP, Kiriakos R (1994), Psychiatric comorbidity in hospitalized adolescent substance abusers. J Am Acad Child Adolesc Psychiatry 33:476–483 Hughes CW, Preskorn SH, Weller E, Weller R, Hassanein R, Tucker S (1990), The effect of concomitant disorders in childhood depression on predicting treatment response. Psychopharmacol Bull 26:235–238 Iacono WG, Carlson SR, Taylor J, Elkins IJ, McGue M (1999), Behavioral disinhibition and the development of substance-use disorders: findings from the Minnesota Twin Family Study. Dev Psychopathol 11:869–900 Jastak S, Wilkinson GS (1984), Wide Range Achievement Test-Revised. Wilmington, DE: Jastak Associates King CA, Ghaziuddin N, McGovern L, Brand E, Hill E, Naylor M (1996), Predictors of comorbid alcohol and substance abuse in depressed adolescents. J Am Acad Child Adolesc Psychiatry 35:476–483 Kovacs M, Paulauskas S, Gatsonis C, Richards C (1988), Depressive disorders in childhood, III: a longitudinal study of comorbidity with and risk for conduct disorders. J Affect Disord 15:205–217 Krueger RF, Caspi A, Moffit TE, Silva PA, McGee R (1996), Personality traits are differentially linked to mental disorders: a multitrait-multidiagnosis study of an adolescent birth cohort. J Abnorm Psychol 105:299–312 Lewinsohn PM, Rohde P, Seeley JR (1995), Adolescent psychopathology, III: the clinical consequences of comorbidity. J Am Acad Child Adolesc Psychiatry 34:510–519 McCracken JT, Cantwell DP, Hanna GL (1993), Conduct disorder and depression. In: Monographs in Clinical Pediatrics, Vol 6: Depression in Children and
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Adolescents, Koplewicz HS, Klass E, eds. New York: Harwood Academic Publishers, pp 121–132 Noam GG, Paget K, Valiant G, Borst S, Bartok J (1994), Conduct and affective disorders in developmental perspective: a systematic study of adolescent psychopathology. Dev Psychopathol 6:519–532 Puig-Antich J (1982), Major depression and conduct disorder in prepuberty. J Am Acad Child Psychiatry 21:118–128 Reich W, Welner Z (1988), Diagnostic Interview for Children and AdolescentsRevised: DSM-III-R Version (DICA-R). St. Louis: Washington University Renouf AG, Kovacs M, Mukerji P (1997), Relationship of depressive, conduct, and comorbid disorders and social functioning in childhood. J Am Acad Child Adolesc Psychiatry 36:998–1004 Riggs PD, Baker S, Mikulich SK, Young SE, Crowley TJ (1995), Depression in substance-dependent delinquents. J Am Acad Child Adolesc Psychiatry 34:764–771 Robins LN (1986), The consequences of conduct disorder in girls. In: Development of Antisocial and Prosocial Behavior: Research, Theories, and Issues, Olweus D, Block J, Radke-Yarrow M, eds. Orlando, FL: Academic Press, pp 385–414 Robins LN, Baber T, Cottler LB (1987), Composite International Diagnostic Interview: Expanded Substance Abuse Module. Linda Cottler, 40 North Kings Highway, Suite 4, St Louis, MO 63108; [email protected] Robins LN, Wing J, Wittchen HU et al. (1988), The Composite International Diagnostic Interview. Arch Gen Psychiatry 45:1069–1077 Rohde P, Lewinsohn PM, Seeley JR (1991), Comorbidity of unipolar depression, II: comorbidity with other mental disorders in adolescents and adults. J Abnorm Psychol 100:214–222 Sack WH, Beiser M, Phillips N, Baker-Brown G (1993), Co-morbid symptoms of depression and conduct disorder in First Nations children: some findings from the Flower of Two Soils project. Culture Med Psychiatry 16:471–486 Spitzer RL (1990), User’s Guide for the Structured Clinical Interview for DSMIII-R. Washington, DC: American Psychiatric Press Spitzer RL, Williams JBW, Gibbon M (1987), Structured Clinical Interview for DSM-III-R. Biometrics Research Department, New York State Psychiatric Institute, 722 West 168th Street, New York, NY 10032 Trull TJ, Sher KJ (1994), Relationship between the five-factor model of personality and Axis I disorders in a nonclinical sample. J Abnorm Psychol 103:350–360 Wechsler D (1981), Manual for the Wechsler Adult Intelligence Scale-Revised. San Antonio, TX: Psychological Corporation Whitmore EA, Mikulich SK, Thompson LL, Riggs PD, Aarons GA, Crowley TJ (1997), Influences on adolescent substance dependence: conduct disorder, depression, attention deficit hyperactivity disorder, and gender. Drug Alcohol Depend 47:87–97
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ABSTRACT Objective: Conduct disorder (CD) and major depression (MDD) frequently co-occur in adolescents, but little is known about the characteristics and functioning of youths, especially females, with both disorders. This study describes the functioning of female adolescents with histories of both CD and MDD. Method: Subjects were selected from an epidemiological sample of 17-year-old female twins based on having a lifetime DSM-III-R diagnosis of MDD and/or CD; control subjects had no history of either disorder. Results: In nearly all domains examined, including measures of academic success (including academic achievement and school adjustment), personality, quality of peer relationships, and high-risk behavior (including substance dependence and early sexual experience), main effects of one or both disorders were found and related to impaired functioning. In addition, interaction effects were found in the areas of substance dependence symptoms (for all classes of substances), negative school-related events, and a personality-based predisposition not to experience positive emotions, indicating that those with both diagnoses were especially impaired. Conclusions: In some domains, histories of MDD and CD interact and relate to particularly severe problems. The implications of these findings for research and treatment, including the high likelihood of substance and school adjustment problems in these youths, are discussed. J. Am. Acad. Child
Adolesc. Psychiatry, 2001, 40(3):299–306. Key Words: conduct disorder, depression, comorbidity, adolescents, females.
Adolescents with either major depression (MDD) or conduct disorder (CD) are at risk for a variety of negative outcomes, both during adolescence and into adulthood, in domains such as academic achievement (e.g., Bardone et al., 1996; Hodges and Plow, 1990), peer relationships (e.g., Cole and Carpentieri, 1990; Renouf et al., 1997), and substance abuse (e.g., Greenbaum et al., 1991; Whitmore et al., 1997). Complicating the effort to understand each of these disorders is the fact that MDD and CD (as well as the more broad domains of depressive symptoms and conduct problems) are often correlated. That is, individuals frequently exhibit both depression and conduct problems, a fact that is striking because many consider these two disorders to represent distinct types of Accepted October 17, 2000. From the Department of Psychology, University of Minnesota, Minneapolis. This study was supported by grants DA05147 from the National Institute on Drug Abuse and AA09367 from the National Institute on Alcohol Abuse and Alcoholism. The authors thank Matt McGue, Ph.D., for his work on the Minnesota Twin Family Study and his comments on an earlier draft of this paper. Reprint requests to Dr. Iacono, Department of Psychology, University of Minnesota, 75 East River Road, Minneapolis, MN 55455. 0890-8567/01/4003-0299䉷2001 by the American Academy of Child and Adolescent Psychiatry.
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behavior—internalizing (depression) and externalizing (CD). Approximately 15% to 25% of youths with CD have comorbid MDD; approximately 15% to 35% of depressed youths exhibit comorbid CD (see review by McCracken et al., 1993). Adolescents with both depression and conduct problems may be at even greater risk for substance dependence (e.g., Riggs et al., 1995) and treatment-seeking (Rohde et al., 1991; Sack et al., 1993) than youths with only one of these problems. They may have lower IQ scores than those with an affective disorder only (Noam et al., 1994), as well as more academic problems than those with disruptive behavior only (Lewinsohn et al., 1995). Poor social competence (Renouf et al., 1997) and maladaptive peer relationships (Asarnow, 1988; Cole and Carpentieri, 1990) are also associated with the co-occurrence of depression and CD. It remains unclear whether the presence of these two disorders together relates to an earlier initiation of sexual activity than one of these disorders alone. Unfortunately, youths with both types of problems may be less amenable to traditional treatments than youths with only one of these disorders (Hughes et al., 1990). Longitudinally, youths with both conduct problems and depression are prone to increased long-term 299
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problems in functioning (including adult criminality), compared with depressed-only youths (Capaldi, 1992; Harrington et al., 1991; Kovacs et al., 1988). Although personality is not a domain of functioning per se, it represents another aspect of an adolescent that likely relates to his or her well-being. It is reasonable to expect that certain aspects of personality would be associated with different types of psychopathology, and studies of late adolescents with affective disorders and CD have confirmed that their personality profiles differ from those of people without these disorders (Krueger et al., 1996; Trull and Sher, 1994). However, far fewer personality differences between disordered and nondisordered individuals emerge when those who have comorbid conditions are excluded (Krueger et al., 1996). The profiles of subjects with the specific pattern of comorbidity evident in this study have not been examined. Females with both depression and conduct problems represent a group that is in particular need of attention. There is indirect evidence that internalizing and externalizing problems may be linked more strongly in females than in males (e.g., Robins, 1986), although the findings to date are far from clear. There is also research describing differences in the problems associated with these disorders in females and males. For example, the relationship among substance abuse, depression, and conduct problems appears to differ for females and males (Bukstein et al., 1992; Clark et al., 1997; Hovens et al., 1994; King et al., 1996; Whitmore et al., 1997), although there is inconsistency in findings regarding the specifics of these differences. Adding to the ambiguity regarding potential gender differences is the fact that many studies (particularly those on CD) include only male subjects. This is the case despite evidence that CD does, in fact, occur in females and does relate to substantial problems in adulthood for those females who are affected by it (e.g., Bardone et al., 1996, 1998). Knowledge about youths with both disorders has significant implications for the existing bodies of literature on depression and conduct problems in adolescents. Studies that examine one of these disorders generally either exclude subjects with additional disorders or ignore potential co-occurring conditions. If subjects with both disorders are indeed different from those with only one in ways that are relevant to the topic under study, results of both types of studies would be problematic. Studies that exclude people with both conditions may be studying an atypical sample. However, if potential co-occurring conditions are simply ignored, the findings may be due to only 300
a subset of subjects (e.g., those who have additional psychological disorders) who are particularly extreme in some way. Thus it is important to elucidate the similarities and differences between people with single conditions and those with co-occurring conditions, especially when two disorders are highly correlated. This study attempted to reduce this gap in research by examining functioning and personality factors in female youths with histories of both depression and CD. In particular, potential interactions between depression and CD were examined, to determine whether youths with both disorders were simply experiencing direct effects of each disorder or whether the interaction of the two disorders was particularly detrimental. METHOD Subjects Subjects were assessed as part of the Minnesota Twin Family Study (MTFS), an epidemiological study of twins and their parents. The MTFS uses a population-based twin ascertainment method in which all female twins who were born in the state of Minnesota during specified years were identified from public birth records. Of these identified families who were eligible, 17.3% refused to participate. There were no significant occupational differences between parents of families who participated and those who declined. After excluding twins who were not suitable candidates for the study (for example, the adolescents were mentally retarded or adopted), the final sample included 337 families of female twins from around the state. The twins were recruited to be approximately age 17 at the time of the family’s visit to the study. For details regarding the design of this epidemiological study, see Iacono et al. (1999). Affected subjects were selected on the basis of having a lifetime diagnosis of MDD and/or CD at either the definite (meeting all DSM-III-R [American Psychiatric Association, 1987] criteria for the disorder) or probable (exhibiting all except one symptom for a DSM-III-R diagnosis) level. A diagnosis was considered present if either the subject herself or her mother reported that the adolescent had experienced enough symptoms. To assess symptoms of MDD, the Structured Clinical Interview for DSM-III-R (SCID) (Spitzer, 1990; Spitzer et al., 1987) was administered to adolescents and a modified version of the Diagnostic Interview for Children and Adolescents-Parent version (DICA-P) (Reich and Welner, 1988) was administered to mothers. To assess symptoms of CD, an MTFS interview that assesses DSM-III-R symptoms of CD was conducted with the adolescents and the DICA-P was administered to mothers. Interviewers had bachelor’s or master’s degrees in psychology or related fields and received intensive training in diagnostic interviewing. The diagnostic interviews were reviewed by teams of advanced clinical psychology doctoral students, who coded the presence or absence of symptoms on the basis of written notes and audiotapes of the interviews. Kappa reliabilities for these diagnoses were as follows: SCID MDD, κ = 0.89; DICA-P MDD, κ = 0.91; MTFS interview CD, κ = 0.85; and DICA-P CD, κ = 0.75. When this method of subject selection was used, approximately 13% (87) of the entire sample met criteria for MDD but not CD, 7% (46) met criteria for CD but not MDD, and 3% (21) meet criteria for both disorders. Thus 31% of subjects with a history of CD
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also had a history of MDD, and 19% of those with a history of MDD also had a history of CD. In no case were two subjects from the same family included in the study. When both twins in a family were affected by a disorder, the subject with the more severe case (more symptoms or symptoms reported by both the mother and the adolescent) was included. When one twin was affected by one disorder and the other twin was affected by both disorders, the twin with both disorders was included. MDD-only subjects who had two or more symptoms of significant antisocial behavior after the age of 15 were excluded. When one twin had CD only while the other had MDD only, both twins were excluded. Control subjects were selected by identifying all families in which neither twin had symptoms of either target disorder, then randomly selecting one adolescent from each of these families. This resulted in the final inclusion of 25 subjects with only CD, 53 subjects with only MDD, 20 subjects with both CD and MDD, and 126 control subjects. Of the 73 subjects with lifetime histories of MDD, 11 (15%) were depressed at the time of the assessment. Ninety-seven percent of the subjects were white, reflecting the demographic makeup of Minnesota at the time they were born (there were no significant group differences on this variable; χ23 = 1.39, p > .05). CD-only subjects were slightly older than CD+MDD subjects at the time of their assessment (mean = 17.7 years for CD-only subjects, compared with 17.3 years for CD+MDD subjects; F3,223 = 3.97, p < .01). Parents’ ages did not differ across groups (F3,435 = 1.94, p > .05). Parental socioeconomic status, as measured by the Hollingshead Four Factor Index of Social Status (Hollingshead, 1975), did not differ across groups (F3,470 = 0.65, p > .05). The average Hollingshead score (4.02) corresponded to occupations such as clerical and sales workers, technicians, and small-business owners. Measures Academic Success. Four subtests of the WAIS-R (Wechsler, 1981) (Vocabulary, Block Design, Picture Arrangement, and Similarities) were administered. Scores were prorated to estimate subjects’ Full Scale IQs. Raw scores on the Wide Range Achievement Test-Revised (Jastak and Wilkinson, 1984) were used as a standardized measure of academic achievement. Adolescents’ reports of overall grade point average (GPA), collected during their interviews, were used as an estimate of grades earned. A composite of negative school-related events (failing classes and getting suspended or expelled) was used as a measure of school adjustment problems. Personality. A modified version of the Multidimensional Personality Questionnaire (A. Tellegen, unpublished, 1982), a self-report personality inventory, was used to assess various aspects of subjects’ personalities. This is a 198-item questionnaire with a 4-point “definitely true” to “definitely false” response format. It assesses 11 primary personality traits (Well-Being, Social Potency, Achievement, Social Closeness, Stress Reaction, Alienation, Aggression, Control, Harm Avoidance, Traditionalism, and Absorption) and yields scores on 3 higher-order factors: Positive Emotionality, or the predisposition to experiencing positive affect (Well-Being, Social Potency, Achievement, and Social Closeness); Negative Emotionality, or the predisposition to experiencing negative affect (Stress Reaction, Alienation, and Aggression); and Constraint, or a measure of behavioral constraint (Control, Harm Avoidance, and Traditionalism). Peer Relationships. Peer relationships were assessed with an MTFS computerized questionnaire that requires that subjects respond to a variety of statements about their peer group by indicating whether “All my friends are like that,” “Most of my friends are like that,” “Just a few of my friends are like that,” or “None of my friends are like that.” Subjects with high scores on the measure of positive peer models tend
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to have friends who work hard to get good grades in school, do their homework and study a lot, are very smart, get good grades in school, and are liked by their teachers, whereas those with high scores on the measure of negative peer models tend to have friends who break rules, drink alcohol, smoke cigarettes or chew tobacco, steal things from others, use drugs, know where to buy drugs, and get into trouble with the police. Alpha reliabilities of each scale were adequate (.78 for positive peer models and .85 for negative peer models). High-Risk Behavior. DSM-III-R substance use disorder symptoms and diagnoses were assigned on the basis of the adolescents’ reports on a modified version of the Substance Abuse Module (Robins et al., 1987, 1988), a supplement to the World Health Organization’s Composite International Diagnostic Interview (Robins et al., 1988). Both counts of the number of dependence symptoms present for each class of substance (nicotine, alcohol and drugs) and actual substance abuse and dependence diagnoses were used in analyses. For the drug dependence symptom count, all symptoms of dependence across all types of drugs were summed (for example, an adolescent with one symptom of cannabis dependence and two symptoms of amphetamine dependence would be assigned a symptom count of three). Substance diagnoses were assigned according to the same procedure outlined above for MDD and CD (under “Subjects”). Substance dependence diagnoses were considered present if the DSM-III-R diagnostic requirements were met at either the definite or probable (missing one symptom) level. Substance abuse diagnoses were assigned only if all diagnostic criteria were met (because only one clinical symptom, plus a duration requirement, is required for these diagnoses). Abuse and dependence diagnoses were combined to create a single substance use disorder variable for each class of substance (nicotine, alcohol, and drugs). Reliabilities of substance use disorder diagnoses exceeded κ = 0.90. During an interview assessing the occurrence and timing of various life events, subjects were asked whether or not they had ever had consensual sexual intercourse. If they responded yes, they were asked the age at which they first did so. Statistical Analyses Two-factor analyses of variance (ANOVAs) were conducted (presence/absence of MDD diagnosis ⫻ presence/absence of CD diagnosis) for all continuous dependent variables to assess for main effects of each disorder and interaction effects. For dichotomous dependent variables (presence or absence of substance use diagnoses and whether or not subjects had initiated sexual activity by the time of their age 17 assessment), logit analyses were conducted to investigate the relationship between MDD diagnosis (present/absent), CD diagnosis (present/ absent), and MDD ⫻ CD interactions and the dependent variable. A separate logit analysis was conducted for each dependent variable; first, a model without interaction effects was compared with the saturated model to determine the importance of the interaction to predicting the dependent variable. Next, models without main effects for each diagnosis were examined to determine the importance of each diagnosis in predicting the dependent variable. RESULTS
The results of all analyses are summarized in Table 1 and Figure 1. Academic Success
No significant main or interaction effects were found in the prediction of subjects’ Full Scale IQ scores or on a 301
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A
B
standardized test of academic achievement. There was a main effect of CD on the prediction of overall GPA. This CD main effect was reflected in the lower GPAs of both CD groups relative to controls, but only the CD+MDD mean GPA was significantly lower in post hoc tests. This pattern, in which a diagnostic main effect is significant but at most one post hoc test involving subgroups differs significantly from controls, appears in several subsequent analyses and illustrates the additional power afforded by ANOVA to detect effects. In addition, there were main effects of both MDD and CD, and an interaction effect of the two disorders, on the prediction of a composite of negative school-related events. Thus it appears that CD alone is related to relatively poor grades, and while each diagnosis is independently associated with increased numbers of negative school-related events, the interaction of both disorders together relates to a particularly high rate of these events. Personality
C
Multidimensional Personality Questionnaire results indicated that main effects for both MDD and CD were present when predicting subjects’ predispositions to experiencing negative emotions and levels of behavioral constraint. When predicting subjects’ predispositions to experiencing positive emotions, we found a main effect for MDD; in addition, an MDD ⫻ CD interaction effect was found. Thus both MDD and CD are related to a predisposition to experience negative emotions and are associated with low levels of behavioral constraint. In addition, MDD is associated with a low level of positive emotionality; MDD and CD also interact in this area and together are associated with a particularly strong predisposition not to experience positive emotions. Peer Relationships
Fig. 1 Number of symptoms of nicotine, alcohol, and illicit drug dependence as a function of the presence or absence of conduct disorder (CD) and major depression (MDD). Because these three symptom count variables were skewed, each was log-transformed (one was added to each subject’s score and the base 10 log was taken) and analyses were repeated. The results were the same as those presented. 䊉 = MDD absent; 䊊 = MDD present.
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Main effects for both MDD and CD were found in the prediction of relatively high levels of negative peer models. In contrast, only a main effect of CD was found in the prediction of low levels of positive peer models. Thus both MDD and CD are independently related to having large numbers of friends who engage in antisocial behavior, while only CD is related to having few friends who engage in prosocial behavior. High-Risk Behavior
When the percentages of subjects with substance use disorder diagnoses (substance abuse or dependence) were J . A M . A C A D . C H I L D A D O L E S C . P S YC H I AT RY, 4 0 : 3 , M A RC H 2 0 0 1
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TABLE 1 Means (and Percentages With Dichotomous Outcomes) for All Diagnostic Groups and ANOVA F Values/Logit Analysis χ2 Values Means (SDs) (and Percentage With Outcomes) for Groups With Psychopathology and Controls a Domain Academic success IQ (Full Scale): mean (SD) WRAT-R (raw score): mean (SD) GPA (overall): mean (SD) No. of negative school eventsc: mean (SD) Personalityd Negative emotionality: mean (SD) Positive emotionality: mean (SD) Constraint: mean (SD) Peer relationshipsd Positive peer models: mean (SD) Negative peer models: mean (SD) High-risk behavior (%) Nicotine dependence Alcohol diagnosis Drug diagnosis Sexual activity by 17
CD + MDD (n = 17–20)
CD Only (n = 21–25)
MDD Only (n = 41–53)
Controls (n = 109–126)
100.20 (11.04) 58.25 (9.52) 2.68a (0.89) 1.25ab (0.79)
94.92 (12.20) 53.64 (9.42) 3.00 (0.87) 0.65ab (0.78)
97.89 (11.00) 59.54 (8.76) 3.15 (0.64) 0.22b (0.47)
97.45 (15.54) 58.07 (9.87) 3.27a (0.69) 0.10a (0.31)
60.30a (12.28) 43.33 (14.27) 34.93ab (13.06)
55.52 (9.71) 50.88 (7.33) 43.44 (13.67)
54.90b (11.14) 50.06 (10.30) 47.41b (10.78)
43.30 (15.90) 66.70 ac (13.92)
43.30 (7.34) 60.95b (11.16)
65.00 ac 60.00 ab 40.00 a 85.00 a
40.00bd 28.00ac 20.00b 64.00b
F/χ2b MDD
CD
MDD ⫻ CD
0.23
0.96
0.31
3.46
3.06
0.93
2.92
8.56**
0.62
18.01***
87.30***
8.10**
50.00ab (10.00) 50.00 (10.00) 50.00a (10.00)
6.43*
8.15**
0.00
4.01*
2.44
4.13*
7.75**
22.82***
2.21
50.55 (11.19) 53.81c (9.12)
50.00 (10.00) 50.00ab (10.00)
0.02
12.49**
0.89
6.21*
38.59***
0.26
13.21cd 9.43bc 7.55a 45.28a
5.56ab 2.38a 0.00ab 21.43ab
5.80* 9.00** 8.98** 12.92***
44.35*** 42.91*** 34.28*** 27.86***
0.01 0.01 2.91 0.00
Note: ANOVA = analysis of variance; CD = conduct disorder; MDD = major depression; WRAT-R = Wide Range Achievement Test-Revised; GPA = grade point average. a Groups with the same subscript are significantly different from each other (p < .05, based on post hoc multiple comparison tests using the Bonferroni correction). b Continuous variables (those with means and SDs) were analyzed with two-factor ANOVAs, with resulting F values reported. Categorical variables (those expressed as percentages) were evaluated with logit analyses, with resulting χ2 values reported. c Because this variable was skewed, a log-transformation was done (1 was added to each subject’s score, then the base 10 log was taken) and the analysis was repeated. The results were identical with those presented above. d Values are T scores derived from the control participants who had a mean of 50 and SD of 10. * p < .05; ** p < .01; *** p < .001.
examined with logit analyses, main effects for MDD and CD were found for all classes of substances (nicotine, alcohol, and drugs). Although no interaction effects were statistically significant, for drug use disorders the interaction of MDD and CD approached significance (p < .09), and for all three disorders the CD+MDD group had an elevated rate of disorder. When the number of symptoms of substance dependence was examined, for all three classes of substances the main effects for MDD (all F1,222 values > 14.15, all p values < .001) and CD (all F1,222 values > 43.25, all p values < .001) were significant. In addition, the three J . A M . A C A D . C H I L D A D O L E S C . P S YC H I AT RY, 4 0 : 3 , M A RC H 2 0 0 1
MDD ⫻ CD interaction effects (all F1,222 values > 12.50, all p values < .001) were significant. The average number of substance dependence symptoms (for each class of substance) reported by subjects with each combination of diagnoses is presented in Figure 1. For each class of substance, all subjects without CD evidenced relatively low numbers of symptoms. However, in the presence of CD, the number of dependence symptoms was highly related to the presence or absence of MDD. Main effects of MDD and CD were found to relate to whether subjects reported having had sexual intercourse by the time of their assessments at age 17. In addition, among 303
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those subjects who had engaged in sexual activity (n = 84), both MDD and CD exerted main effects on the age at first intercourse (F1,81 = 6.06, p < .05 for MDD; F1,81 = 22.91, p < .001 for CD). No interaction of MDD and CD was found (F1,81 = 0.64, p > .05). Among subjects who reported having had sex, those with histories of both disorders initiated sexual activity at age 14.76 (SD = 1.20), whereas those with only CD initiated at 15.44 (SD = 1.03), those with only MDD initiated at 15.92 (SD = 0.93), and those with neither disorder initiated at 16.26 (SD = 0.59). Thus both MDD and CD are associated with sexual activity by age 17, and among subjects having engaged in sexual activity by age 17, both disorders are associated with sexual activity at particularly young ages. Effects of Acute Depression
Because it was possible to determine which subjects were depressed at the time of their assessment, acutely depressed participants (n = 11) were excluded and all analyses were repeated. The results did not change appreciably. In two instances, findings that had been statistically significant were reduced to trends (MDD main effects for positive and negative emotionality; p values < .10). One additional main effect for MDD was found (score on the Wide Range Achievement Test-Revised; F1,212 = 4.40, p < .05). DISCUSSION
The results of this study suggest that both depression and CD are related to significant difficulties in functioning, as well as particular personality characteristics, for female adolescents. Because depression and CD frequently have detrimental main effects on the same areas of functioning, these disorders sometimes interact to produce especially poor outcomes. This is particularly the case with respect to substance dependence: the combination of these two disorders is associated with particularly high numbers of symptoms (more than would be expected considering only the effects of each disorder alone). Although a similar trend was seen for substance disorder diagnoses, the interaction effect was not significant. The difference in the outcome of these two analyses may derive from the increased power to detect an interaction effect in the analysis if continuous, as opposed to categorical, data are used. Depression and CD also interact in relation to school adjustment and the personality dimension of positive emotionality. Each disorder alone is related to increased numbers of negative school-related events such as sus304
pension and failure of classes; together, these disorders are related to even more problems of this sort than would be expected on the basis of only the main effects of each disorder. This is consistent with previous research indicating that depression and disruptive behavior together are related to more school problems than disruptive behavior alone (Lewinsohn et al., 1995). Both disorders together are also associated with a lowered predisposition to the experience of positive emotions, even though when the disorders are considered separately only depression is related to low scores on this dimension. In other domains, however, depression and CD relate to difficulties in functioning but do not interact to produce impairments beyond what would be expected if one were considering the presence or absence of each disorder separately. When considering certain dimensions of personality (negative emotionality and behavioral constraint), peer relationships (the predominance of negative peer models), and high-risk behavior (early sexual behavior), both depression and CD exert main effects that relate to problems in these areas. Thus, previous studies’ findings that youths with both disorders have maladaptive peer relationships (Asarnow, 1988; Cole and Carpentieri, 1990) may simply be due to the presence of each disorder independently and not to any interaction between the disorders. In contrast, overall GPA and the presence of few positive peer models are uniquely associated with the effects of CD. Depression is uniquely associated with low levels of positive emotionality (as discussed above, depression and CD also interact in this area). This study’s analysis of a group of females with conduct problems (both with and without depression) is relatively rare; therefore, several aspects of the findings merit brief discussion. First, the domains in which depression and CD are associated with problems in functioning for females are similar to those that would likely be found in males with these disorders; that is, they are similar to those found in males with conduct problems, with or without comorbid conditions. Second, although both disorders are related to impaired functioning in a variety of domains, when substance use problems are examined the interaction of these disorders is associated with a level of pathology that is quite striking. The relationship among depression, conduct problems, and substance use problems in females raises cause for serious concern and therefore merits further study, particularly because there may be gender differences in this relationship (e.g., Clark et al., 1997; Whitmore et al., 1997) that J . A M . A C A D . C H I L D A D O L E S C . P S YC H I AT RY, 4 0 : 3 , M A RC H 2 0 0 1
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render findings based on samples of males not applicable to females. The findings of this study have implications for research focused on one or the other of these disorders. With approximately one fifth of those with a history of depression also having a history of CD and approximately one third of those with CD also having a history of depression, substantial numbers of youths apt to be included in studies of each single disorder likely have the other disorder. It is important that, whenever possible, researchers either study “pure” groups (i.e., without co-occurring conditions, resulting in an unrepresentative sample of those with the disorder) or carefully incorporate the other disorder into the research design. Because these disorders frequently relate to impairments in the same domains (and sometimes interact as well), studies that simply ignore potentially co-occurring disorders may therefore obscure the true effects of either disorder. Limitations
Several limitations of this study should be noted. First, it should be remembered that subjects in this study were selected from an epidemiological sample of adolescents. Therefore, cases of CD and depression may have been less severe and/or impairing than cases of these disorders found in clinic settings. It is, however, striking that despite the nonclinical nature of this sample, subjects in this study evidenced significantly impaired functioning in a variety of domains. In addition, subjects in this study had histories of these disorders; they did not necessarily have active symptoms at the time of assessment, nor did they necessarily have both disorders at the same time. Subjects also may have had other psychiatric disorders; because of the population-based nature of this sample, those other disorders represent what would naturally occur in adolescents with these disorders. It is also possible that some of the nonsignificant findings associated with the smaller diagnostic groups can be attributed to these groups having relatively fewer subjects. It is crucial to note that this study did not address the issue of causality. Thus it is not known whether the disorders caused the functional problems, the functional problems precipitated the development of the disorders, or some third factor (e.g., temperament) underlies both the disorders and the functional problems. Finally, subjects in this study were primarily white. Although this reflects the demographic makeup of Minnesota at the time they were born, it may limit the applicability of the findings to other groups. J . A M . A C A D . C H I L D A D O L E S C . P S YC H I AT RY, 4 0 : 3 , M A RC H 2 0 0 1
Clinical Implications
It is apparent that youths presenting with either disorder need to be carefully assessed for the other disorder. For those youths found to have both disorders, thoughtful treatment of both problems, regardless of which is the presenting problem, will likely be necessary. Currently, clinicians must rely on treatments developed for youths with only one of these two disorders, although these may be less effective in treating people with both disorders (e.g., Hughes et al.,1990). Fortunately, there is some indication that successfully treating one disorder may result in improvements in the other (Puig-Antich, 1982). Clinicians must be aware that the course of the “primary” disorder may be altered by the presence of the other disorder. For example, it has been suggested that the outcomes of depressed children with CD closely resemble those of nondepressed children with CD (and do not as closely resemble those of depressed children without CD) (Harrington et al., 1991). It must be remembered that substance use problems are the norm, not the exception, in this group. Interventions aimed at changing the peer groups of these youths, their school-related behavior, and their patterns of substance use will be appropriate for many clients. Behavior changes in these areas will likely complement the treatment of the psychopathology and prevent other potential associated problems (e.g., sexually transmitted diseases, school dropout). In addition, identifying youths with one disorder who are particularly at risk for developing the other disorder could aid in prevention efforts. More information about the potentially unique etiology of the co-occurrence of depression and CD would also aid in the development of effective prevention and treatment strategies. REFERENCES American Psychiatric Association (1987), Diagnostic and Statistical Manual of Mental Disorders, 3rd edition-revised (DSM-III-R). Washington, DC: American Psychiatric Association Asarnow JR (1988), Peer status and social competence in child psychiatric inpatients: a comparison of children with depressive, externalizing, and concurrent depressive and externalizing disorders. J Abnorm Child Psychol 16:151–162 Bardone AM, Moffitt TE, Caspi A, Dickson N, Silva PA (1996), Adult mental health and social outcomes of adolescent girls with depression and conduct disorder. Dev Psychopathol 8:811–829 Bardone AM, Moffitt TE, Caspi A, Dickson N, Stanton WR, Silva PA (1998), Adult physical health outcomes of adolescent girls with conduct disorder, depression, and anxiety. J Am Acad Child Adolesc Psychiatry 37:594–601 Bukstein OG, Glancy LJ, Kaminer Y (1992), Patterns of affective comorbidity in a clinical population of dually diagnosed adolescent substance abusers. J Am Acad Child Adolesc Psychiatry 31:1041–1045
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