Associations Between Clinic-Referred Boys and Their Fathers on Childhood Inattention-Overactivity and Aggression Dimensions

Transcription

1 Journal of Abnormal Child Psychology, Vol. 25, No. 6, 1997, pp Associations Between Clinic-Referred Boys and Their Fathers on Childhood Inattention-Overactivity and Aggression Dimensions Jan Loney,1,4 Carl E. Paternite,2 Joseph E. Schwartz,1 and Mary Ann Roberts3 Received December 23, 1996; revision received April 15, 1997; accepted April 16, 1997 The question asked in this study of 70 clinically referred 6- to 12-year-old boys with behavior problems was whether or not childhood inattention-overactivity and aggression are transmitted specifically from biological fathers to sons. Fathers' self-reported childhood inattentionoveractivity on a retrospectively valid measure was exclusively associated with parents' ratings of their sons' current attention problems on the Mothers' Operational Measure for Subgrouping (MOMS), the Revised Child Behavior Checklist (RCBCL), and an approximated DSM-IV inattention dimension. Fathers' self-reported childhood aggression was not associated with ratings of their sons' aggression on the MOMS or DADS (a parallel instrument for fathers), nor on DSM-III oppositional or conduct disorder dimensions, but it was exclusively associated with RCBCL ratings of sons' aggressive and delinquent behavior. None of the nonspecific correlations (father inattention-overactivity with son aggression or father aggression with son inattention-overactivity) was significant. KEY WORDS: Inattention-overactivity; aggression; family transmission; differential validity; retrospective validity. In order to understand childhood disruptive psychopathology, it is important to know if hyperactivity (attention deficit disorders) and aggression (oppositional and conduct disorders) are transmitted from parents to children. A relatively simple approach to questions about the generational transmission of childhood disruptive disorders is to interview the parents of a sample of diagnosed child probands about their own childhood symptoms. Iwo family studies of this type have reported the percentage of childhood ^tate University of New York, Stony Brook, Stony Brook, New York Miami University, Oxford, Ohio. 3University of Iowa, Iowa City, Iowa. 4Address all correspondence to Jan Loney, Department of Psychiatry and Behavioral Science, Putnam Hall, South Campus, State University of New York, Stony Brook, Stony Brook, New York hyperactive and aggressive problems or disorders in the fathers of boys with attention deficit (ADD) and conduct disorders (CD). In a study of 22 six- to seventeen-year-old ADD boys diagnosed by Diagnostic and Statistical Manual of Mental Disorders (3rd ed.) (DSM-III; American Psychiatric Association [APA], 1980) criteria, Biederman et al. (1986) found that 45% had fathers who also had ADD in childhood, compared to % of the fathers of 20 normal controls. There was no association between fathers' and sons' CD. Subsequent reports from the Biederman group on larger samples diagnosed by the revised DSM-III (DSM-III-R; APA, 1987) criteria have not provided diagnostic data on both attention-deficit hyperactivity disorder (ADHD) and CD for fathers of both ADHD and CD boys. Frick, Lahey, Christ, Loeber, and Green (1991) carried out a family study of 177 seven- to twelve /97/ S12.50/ Plenum Publishing Corporation

2 500 Loney, Paternite, Schwartz, and Roberts year-old clinic-referred boys diagnosed by DSM-III- R criteria. They found that 48% of boys with both ADHD and CD and 40% of boys with ADHD but not CD had fathers who were hyperactive before age 18, compared to only 18% of pure CD boys and 22% of nondisruptive psychiatric control boys. Although there were similar differences between early symptoms of conduct disorder in the fathers of boys with and without CD, the CD and non-cd boys also differed in race and socioeconomic status, and after statistical controls were applied for those differences, the relationship between fathers' and sons' CD was not significant. Frick et al. found no nonspecific differences that is, ADHD boys with and without comorbid CD did not differ in the early hyperactivity of their fathers, and CD boys with and without ADHD did not differ in the early conduct problems or substance use of their fathers. These studies have shed light upon the generational transmission of childhood hyperactive and aggressive disorders, but several problems have obscured their interpretation. One problem is that diagnosing childhood ADHD and CD from the retrospective self-reports of adults is difficult (Henry, Moffitt, Caspi, Langley, & Silva, 1994; Shaffer, 1994). Another problem is that mothers of the ADHD child probands have been relied upon for the childhood diagnostic information on some (Biederman et al., 1986) or all (Frick et al., 1991) of the biological fathers of the probands. Such studies almost surely contain missing or false negative diagnoses based on information from mothers who were unfamiliar with their husbands' behavior as children. They may also contain false positive diagnoses from mothers who were negative toward absent fathers. These biases combine to increase diagnostic errors and thereby to jeopardize the validity of conclusions about the generational transmission of disruptive disorders. The present study was based on a two-factor model (Loney, Kramer, & Milich, 1981; Loney, Langhorne, & Paternite, 1978; Loney, Kramer, & 5 In most research on the two-factor model (e.g., Loney & Milich, 1982), the hyperactivity factor is significantly correlated primarily with inattentive and small motor symptoms (e.g., fidgetiness). In contrast, large motor hyperactive and impulsive symptoms (e.g., running about) are often correlated with both the hyperactivity and aggression factors (i.e., they are divergently invalid or contaminated). For this reason, and in order to avoid confusion with the hyperactive-impulsive subtype of ADHD in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; APA, 1994), the hyperactivity factor of the two-factor model is referred to here as the inattention-overactivity factor. Whitten, 1989) which postulates that although hyperactivity 5 (i.e., inattention-overactivity) and aggression 6 can be highly correlated, especially when measured with teacher rating scales, and although their associated disorders (ADHD and ODD/CD) often co-occur, especially in children referred to clinics, they are conceptually independent behavioral dimensions in terms of their antecedents, correlates, and consequences (Hinshaw, 1987). Subsequently, similar two-factor models have been derived and tested by other investigators (McGee, Williams, & Silva, 1984; Taylor, Schachar, Thorley, & Wieselberg, 1986). The question asked in the current study was whether the inattention-overactivity and aggression dimensions of childhood are transmitted from fathers to sons and, if they are, whether that transmission is specific or general. If the hypotheses of the two-factor model are correct, the transmission of childhood dimensions would be exclusive and specific that is, men who were more inattentive-overactive as children would have offspring who were more inattentive-overactive (but not more aggressive), whereas men who were more aggressive as children would have offspring who were more aggressive (but not more inattentive-overactive). In order to improve the assessment of childhood disruptive dimensions in biological fathers in this study, all information about biological fathers was obtained directly from them (the family study method), instead of partially or entirely from their spouses (the family history method). For what is believed to be the first time, fathers' recollections of their childhood inattentive-overactive and aggressive symptoms were obtained with an instrument (the Measure of Behavior Dimensions-Retrospective, or MBD-R; Loney & Kramer, 1992) that is retrospectively valid. That is, the childhood symptoms reported by adult men on the MBD-R are significantly related to their actual childhood symptom dimensions. In addition, the measures used in this study to operationalize the childhood dimensions of the two- 6 The items of some two-factor aggression measures (e.g., the WA Conners; Loney & Milich, 1982) describe primarily oppositional behaviors (e.g., temper outbursts, defiance), and some investigators have renamed these aggression subscales to reflect more accurately the apparent content of the items. However, because these renamed "oppositional" or "defiant" subscales correlate significantly with aggression toward peers in elementary school settings (e.g., hitting, taunting, and gesturing), as well as with noncompliance toward teachers (Nolan & Gadow, 1994), they are referred to here as aggression subscales.

3 Inattentive and Aggressive Fathers and Sons 501 factor model in fathers (the MBD-R, Loney & Kramer, 1992) and in sons (the Mothers' Operational Measure for Subgrouping, or MOMS; Loney, 1984; and its parallel for fathers, the DADS) are both convergently and divergently valid. That is, measures of inattention-overactivity are significantly related only to an inattention-overactivity criterion, whereas measures of aggression are related only to an aggression criterion. This study focused on the transmission from one generation to another of childhood rather than adolescent or adult disruptive dimensions, thus avoiding the problems that are associated with the measurement of residual or adult ADHD (Shaffer, 1994). Mothers' and fathers' ratings of their sons' behaviors were used separately as dependent variables to tap two adults' perspectives on the sons' symptoms and to provide cross-informant correlations between the fathers' recollections of their own symptoms and the mothers' ratings of the sons. METHOD Participants In an investigation of methods for subgrouping behavior problems, data were gathered on 132 sixto twelve-year-old boys who had been consecutively referred between 1984 and 1986 to three universitysponsored outpatient child mental health clinics in New York (n = 76), Ohio (n = 41), and Michigan (n = 15). Boys with IQs of less than 70 or with evidence of organic impairment or pervasive developmental disorders were excluded. In addition, boys were excluded if they did not obtain a T-score greater than 59 (84th percentile or 1 standard deviation above the mean) on at least one of the externalizing symptom factors from the mother or teacher form of the Child Behavior Checklist (CBCL; Achenbach & Edelbrock, 1983). The standard CBCL T-score that is considered to define significant behavioral pathology is 70 (98th percentile or 2 standard deviations above the mean). All participating boys and their parents gave informed consent. For a detailed description of this sample, see Paternite, Loney, and Roberts (1995). Of the 131 families for whom data were available on their living circumstances at the time of evaluation, 82 consisted of both biological parents and their sons living together. The 85% (n = 70) of these 82 biological families for whom MBD-R data were available from the biological father formed the sample for the current study. The number of subjects for reported analyses ranges from 63 to 70 due to missing data within specific pairs of measures. Biological parents (predominantly fathers) who were not living with their sons were excluded. Measures Parents in the overall investigation completed numerous interviews, questionnaires, and rating scales concerning their children's behavior, their own behavior as children, and the family environment. Two-factor measures of parent and child psychopathology were obtained by means of the Multiple Symptom Subgrouping Method (MSSM; Roberts, Milich, Loney, & Caputo, 1981). The MSSM-derived measure of parents' childhood inattention-overactivity and aggression was the Measure of Behavior Dimensions-Retrospective (Loney & Kramer, 1992). The MSSM-derived measures of sons' current inattention-overactivity and aggression were the motherrated Mothers' Operational Measure for Subgrouping (Loney, 1984) and its father-rated version (DADS). Offspring measures based on two additional diagnostic models were included: the Revised Child Behavior Checklist (RCBCL; Achenbach, 1991) and the third and fourth versions of the DSM. The Multiple Symptom Subgrouping Method The Multiple Symptom Subgrouping Method (Roberts et al., 1981) was derived from previous studies of the two-factor model (Loney et al., 1978). It is a 32-item alphabetical checklist with which adult informants (parents, teachers, and clinicians) can directly describe inattentive, hyperactive, and aggressive behaviors. For all measures, checked items are scored as 1 and unchecked items are scored as 0. The measures used in the current study to operationalize the childhood inattention-overactivity () and aggression () factors in fathers and sons were obtained by administering the MSSM checklist to parents twice, giving different instructions for each administration. Fathers and mothers were separately asked to describe "your son as he is now" and "yourself at the same age as your son is now." For each measure, a different set of items was selected on the

4 502 Loney, Paternite, Schwartz, and Roberts basis of individual item validities, using a method previously employed in the construction of the WA (Inattention-Overactivity with Aggression) Conners Teacher's Rating Scale (Loney & Milich, 1982). Fathers' Recollections of Their Own Childhood Symptoms. The two sets of items from the MSSM that were used in this study as measures of the fathers' childhood and symptoms were derived in a study of 155 clinically diagnosed hyperkinetic/mbd boys who were referred for outpatient psychiatric evaluation between ages 4 and 12 and followed up as young adults between ages 21 and 23. In that derivation study (Loney & Kramer, 1992), the previously hyperkinetic young adult men were asked to describe themselves on the MSSM symptom checklist as they remembered having been between ages 8 and. Correlation coefficients were computed between the young men's recollections of their childhood symptoms and the and factor scores that had actually been assigned to the boys more than 9 years previously based on judges' ratings of the boys' childhood symptoms from charts (Loney et al., 1978). Seven of the 32 MSSM symptom items were significantly correlated with childhood but not with childhood, and they were therefore considered to have convergent and divergent validity as retrospective measures of childhood inattentionoveractivity. Four of the 32 MSSM symptom items were significantly correlated with childhood but not with childhood, and they were therefore considered to have convergent and divergent validity as retrospective measures of childhood aggression. Together, the seven-item subscale (can't concentrate, distractible, excitable, fidgety, messy, moves in bursts, and wiggles) and the four-item subscale (irritable, mean, quick-tempered, and rebellious) are called the Measure of Behavior Dimensions-Retrospective. The long-term test-retest reliabilities of the MBD-R and subscales were.46 and.52, respectively, in a subset of 75 of the previously hyperkinetic young men who were followed up again at ages 28 to 32. Mothers' Descriptions of Their Sons' Symptoms. The two sets of items from the MSSM used in this study as measures of the sons' current and symptoms were derived in a different sample of 97 boys who were consecutively referred for outpatient psychiatric evaluation between ages 6 and 12. In that derivation study (Loney, 1984), correlations were computed between the mothers' descriptions of their sons' current symptoms on the MSSM checklist and and factor scores based on judges' ratings of chart material describing the sons' symptoms. Items that were convergently and divergently valid measures of the and factors were selected. The selection procedure resulted in a five-item subscale (can't concentrate, distractable, fidgety, immature, spills things) and a five-item subscale (explosive, irritable, quick-tempered, rebellious, starts fights) for mothers' ratings of their sons. Together, these two subscales are called the Mothers' Operational Measure for Subgrouping. The long-term testretest reliabilities of the MOMS and subscales were.34 and.58, respectively, in a subset of 72 of the boys who were followed up 2 years later. Fathers' Descriptions of Their Sons' Symptoms. The items of the MOMS subscale were also convergently and divergently valid for fathers' descriptions of their sons. However, the items of the MOMS subscale were not valid for fathers, and an alternative subscale for sons' inattention-overactivity could not be derived from the fathers' responses to the MSSM items in that study, because too few of the items were convergently and divergently valid. For the current investigation, the fathers' responses to the MOMS items were utilized as a measure of the fathers' descriptions of their sons' current aggressive behavior and referred to as the DADS subscale. Additional Parental Measures of Sons' Symptoms Each parent independently completed the Revised Child Behavior Checklist (Achenbach, 1991) to describe his or her referred son. Three RCBCL factor scores (attention problems, delinquent behavior, and aggressive behavior) were used as dimensional offspring measures in this study. Parent(s) were interviewed by a trained member of the research team (a child psychiatrist, clinical psychologist, or advanced clinical psychology graduate student) using the highly structured DSM-III version of the Diagnostic Interview for Children and Adolescents, Parent Version (DICA-P; Herjanic, 1981), which provides a basis for making reliable DSM-III diagnoses (Welner, Reich, Herjanic, Jung, & Amado, 1987). A severity prerequisite was applied to each DICA-measured symptom before that symptom was recorded as present. Dimensional scores for the inattention and hyperactivity-impulsivity criteria of DSM-IV were approximated according to algorithms

5 Inattentive and Aggressive Fathers and Sons 503 Table I. Hierarchical Regression Analyses Predicting MOMS Mother-Rated Child Inattention-Overactivity and Aggression Scores, and DADS Father-Rated Child Aggression Scores, from Father MBD-R Scores for Inattention-Overactivity () and Aggression (AO)" Dependent variable Inattention-overactivity (MOMS) Aggression (MOMS) Aggression (DADS) Independent variable (father MBD-R) ( x ) ( x ) ( x ) Simple 6 r.25* Partial' r 22 e Multiple** R "N = 68 for all analyses. MBD-R = Measure for Behavior Dimensions-Retrospective; MOMS = Mothers' Operational Measure for Subgrouping; DADS = Father-report version of the MOMS. *The simple rs for and are the correlations of each of the independent variables with the dependent variable at Step 1 in the regression analysis. The partial rs for and are the correlations of each of these independent variables with the dependent variable at Step 2, after the other independent variable ( or ) has been entered on the previous step. The partial r for the interaction ( x ) is its correlation with the dependent variable after and have been entered on the two previous steps. d The multiple Rs reported for and reflect the inclusion of both variables, and the final multiple R reflects the inclusion of,, and the interaction term ( x ). e p <.05, one-tailed that combined for the inattention dimension six relevant questions from the DSM-III version of the DICA-P with one question from the MOMS, and that combined for the hyperactivity-impulsivity dimension seven relevant questions from the DSM-III version of the DICA-P with one question from the RCBCL (Paternite, Loney, & Roberts, 1996). For oppositional and aggressive and nonaggressive conduct disorders, separate dimensional scores were obtained by summing responses for each set of relevant DSM- III criteria. RESULTS Two hierarchical regression analyses were carried out for each of the sons' subscales, factors, or dimensions, using the fathers' ratings of their own childhood and on the MBD-R as predictor variables. One of each pair of analyses entered the fathers' scores first and their scores second; the other analysis entered the fathers' scores first and their scores second. Step 1 of each analysis tested the significance of the simple correlation between the fathers' first MBD-R measure and the sons' dependent measure. Step 2 of the analysis tested the significance of the partial correlation between the fathers' second MBD-R measure and the sons' dependent measure with the first MBD-R measure held constant. The second step of these analyses addressed two questions: (1) Was either of the fathers' MBD-R subscales an exclusive predictor of the given sons' measure? (2) If there was an association between a pair of fathers' and sons' measures, was that association specific? A given fathers' MBD-R measure was an exclusive predictor of the dependent variable (sons' subscale, factor, or dimension) under the following conditions: (1) Its partial correlation with the dependent variable was significantly different from zero that is, it was still significantly correlated with the sons' measure after the fathers' other MBD-R measure was held constant, and (2) the partial correlation of the fathers' other MBD-R measure with the sons' measure was not significantly different from zero, and therefore that other MBD-R measure was either irrelevant to predicting the dependent variable (not significant in either the first or the second position) or redundant once its correlation with the alternative MBD-R score was held constant (significant in the first position, but not in the second). A specific association was one between fathers' and sons' lo-related measures (i.e., inattention, attention problems, hyperactivity-impul-

6 504 Loney, Paternite, Schwartz, and Roberts Table II. Hierarchical Regression Analyses Predicting Mother- and Father-Rated RCBCL Attention Problems, Delinquent Behavior, and Aggressive Behavior, from Father MBD-R Inattention-Overactivity () and Aggression ()a Dependent variable Independent variable (father MBD-R) Simple* r Partial" r Multiple'' R Attention problems by mother Attention problems by father Delinquent behavior by mother Delinquent behavior by father Aggressive behavior by mother Aggressive behavior by father ( x ) ( x ) ( x ) ( x ) ( x ) ( x ) e.24*.01.24*.14 2\e.12.2(f.24e yf e * ,25e e ' T 21e.29.36*.36".3T /.39'.40' "N = 65 to 69 for all analyses. MBD-R = Measure for Behavior Dimensions Retrospective; RCBCL = Revised Child Behavior Checklist (Achenbach, 1991). ''See Note b below Table I. csee Note c below Table I. dsee Note d below Table I. ep <.05, one-tailed. fp <.01, one-tailed. sivity) or between fathers' and sons' -related measures (i.e., aggression, delinquency, oppositional and conduct problems). In contrast, a nonspecific association was one between fathers' and sons' or between fathers' and sons'. The third step in each of the hierarchical analyses entered a cross-product term ( x ) in order to test whether the interaction of fathers' childhood and predicted the sons' subscale, factor, or dimension. A significant interaction meant that the role of one predictor varied at different levels of the other predictor. In categorical terms, an interaction can indicate that the comorbidity of paternal and is associated with the criterion variable. Tables I through III present simple-, partial-, and multiple-correlation coefficients. Significance tests were one-tailed at the p <.05 level. Table I presents the results of hierarchical analyses of the two-factor measures of sons. Fathers' childhood was an exclusive and specific predictor of MOMS in sons. Fathers' and were both irrelevant to the prediction of MOMS and DADS in sons. There were no significant interactions between fathers' and on any of the MOMS or DADS subscales. Table II presents the results of hierarchical analyses of the RCBCL measures of sons. Fathers' childhood was an exclusive and specific predictor of sons' RCBCL attention problems as rated by both mothers and fathers. Fathers' childhood was an exclusive and specific predictor of sons' RCBCL aggressive behavior as rated by both fathers and mothers and of sons' RCBCL delinquent behavior as rated by mothers. Fathers' childhood was not a significant predictor of sons' RCBCL delinquent behavior as rated by fathers after fathers' was held constant (partial r =, p =.08), so it was not an unequivocally exclusive predictor. There were no significant interactions between fathers' and on any of the RCBCL factors. Table III presents the results of hierarchical analyses of approximated DSM-IV DICA-P inattention and hyperactivity-impulsivity dimensions (Paternite et al., 1996) and of DSM-III DICA-P oppositional, aggressive conduct, and nonaggressive

7 Inattentive and Aggressive Fathers and Sons 505 Table III. Hierarchical Regression Analyses Predicting DSM-IV Attention Deficit Hyperactivity Disorder (ADHD) Dimensions and DSM-III Oppositional Disorder/Conduct Disorder (OD/CD) Dimensions from Father MBD-R Inattention-Overactivity () and Aggression () Dependent variable DSM-IV inattention DSM-IV hyperactive impulsive DSM-III OD DSM-III CD-Agg DSM-III CD-NonAgg Independent variable (father MBD-R) ( x ) ( x ) ( x ) ( x ) ( x ) Simple* r.22 s Partial r * -.15 * ' Multiple 1 * R "N = 69 to 70 for all analyses. MBD-R = Measure for Behavior Dimensions-Retrospective; CD-Agg = CD aggressive symptoms; CD-NonAgg = CD nonaggressive symptoms. *See Note b below Table I. c See Note c below Table I. rf See Note d below Table I. 'p <.05, one-tailed..27 e.21 e 31 e conduct dimensions. Fathers' childhood was an exclusive and specific predictor of the sons' DSM-IV inattention dimension. There was also a significant interaction between fathers' and in predicting DSM-IV inattention. Examination of this interaction at various levels of fathers' MBD-R and indicated that the few fathers with very high scores on childhood and/or childhood had sons with the highest scores on DSM-IV inattention. Fathers' childhood and were irrelevant to the prediction of sons' DSM-IV hyperactivity-impulsivity, DSM-III oppositional, and DSM-III aggressive and nonaggressive conduct dimensions (there were no significant simple or partial associations between either fathers' childhood or and any of the latter DSM dimensions). There was a significant interaction between fathers' and in the prediction of the sons' DSM-III aggressive conduct disorder dimension. Examination of this interaction at various levels of fathers' MBD-R and indicated that the few fathers with very high scores on childhood or childhood had sons with the highest scores on the DSM-III aggressive conduct dimension. The MBD-R has not been shown to be retrospectively valid for women, but in order to provide preliminary information about disruptive childhood psychopathology in women, a parallel set of hierarchical analyses was carried out between the childhood dimensions of mothers and their sons. For the two-factor measures, there were no significant correlations between mothers' childhood or and MOMS or MOMS or DADS. For the RCBCL, neither mothers' nor was significantly correlated with any of the sons' attention problems, delinquent behavior, or aggressive behavior factors. For the approximated DSM-IV dimensions, neither mothers' nor was correlated with sons' inattention, but mothers' childhood was an exclusive and specific predictor of sons' hyperactivity-impulsivity (for MBD-R, partial r = 0.32, p <.01, and for MBD-R, partial r = 0.15, n.s.). Neither mothers' nor was significantly correlated with any of the sons' DSM-III oppositional, aggressive, or nonaggressive conduct disorder dimensions. There were no significant interactions between mothers' and on any of the sons' scores. It was recognized that a disproportionate number of fathers who had the most severe adult psychopathology (e.g., substance abuse and antisocial personality disorders) and who presumably had been the most aggressive children were probably excluded from the current study because they were

8 506 Loney, Paternite, Schwartz, and Roberts not living with their biological sons. If aggression is transmitted from fathers to sons, some of the most aggressive sons could therefore have been excluded from the analyses. To test this possibility, the mothers' MOMS ratings of their sons' inattention-overactivity and aggression were compared between two groups: the boys included in the current study sample (those living in two-parent biological families) and the boys excluded from the study (those living with a biological parent and a nonbiological parent, with one biological parent, or with nonbiological parent(s) or relatives). For MOMS inattention-overactivity, differences among the included and excluded boys were not significant (Ms = 3 for excluded boys and 3.12 for included boys; t = 0.23, df = 114, n.s.), and therefore the results for inattention-overactivity should not be biased because of excluded biological fathers. However, for MOMS aggression, the mothers of excluded boys rated their sons as significantly more aggressive than mothers of included boys (Ms = 2.38 for excluded boys and 1.74 for included boys; t = 2.12, df = 114, p =.04). Therefore, nonsignificant results for dependent variables that concern aggression should be interpreted with this probable sampling bias in mind. DISCUSSN Among the two-factor measures, fathers' childhood inattention-overactivity on the MBD-R was an exclusive and specific predictor of the mothers' descriptions of their sons' current inattention-overactivity on the MOMS. In contrast to the findings for MOMS inattention-overactivity, neither mothers' nor fathers' descriptions of their sons' current aggression on the MOMS or DADS was significantly correlated with fathers' recollections of either their own aggression or their own inattention-overactivity in childhood. Thus, the current findings for the two-factor measures are only partially compatible with hypotheses derived from the two-factor model (Loney et al., 1978, 1981, 1989), which correctly predicted that childhood inattention-overactivity would be exclusively associated in fathers and sons, and that the association would be specific (that is, that inattention-overactivity would not be significantly associated with aggression across generations), but which incorrectly predicted that childhood aggression would also be associated in fathers and sons. However, the findings reported here for the twofactor measures correspond to those of the Biederman et al. (1986) and Frick et al. (1991) family studies and to those of Barkley, DuPaul, and McMurray (1990), all of which suggest that childhood attention deficit disorders are associated across generations, but that childhood oppositional and conduct disorders are not. These findings linking childhood inattention-overactivity but not childhood aggression in fathers and sons are compatible with the common belief that the etiology of hyperactivity is primarily biological (Barkley, 1990), whereas aggression has important environmental or psychosocial mediators (Patterson, DeBaryshe, & Ramsey, 1989). However, possible relationships between fathers' and sons' aggression may have been attenuated, because included boys were rated by their mothers as less aggressive than excluded ones. Although the three sets of offspring measures covered similar symptoms and were reported by the same informants, it is still noteworthy that the findings for the two-factor model (Loney, 1984), the RCBCL (Achenbach, 1991), and the DSM-IV diagnostic dimensions from the DICA-P all indicate that there was an exclusive and specific relationship between fathers' inattention-overactivity in childhood and the current attention deficits of their biological sons who had been referred for behavior problems. Those findings suggest that childhood attention problems are transmitted across generations from fathers to sons, and that they are transmitted specifically, rather than as part of a broader disruptive or externalizing dimension. The findings across the three assessment models were inconsistent regarding the relationship between fathers' and sons' aggressive dimensions. The twofactor and DSM-III measures provided no evidence for generational transmission of childhood aggression, whereas the RCBCL findings indicated that fathers' and sons' aggressive and delinquent behaviors were exclusively and specifically related. In general, past studies have indicated a stronger genetic association for hyperactivity than for aggression, although few studies have used divergently valid measures. Twin studies of the RCBCL have indicated that the attention problem, delinquent, and aggressive behavior factors are genetically transmitted (e.g., Edelbrock, Rende, Plomin, & Thompson, 1995), although RCBCL delinquent behavior may also have substantial environmental components. It is unclear why the three diagnostic models (and the findings for the fa-

9 Inattentive and Aggressive Fathers and Sons 507 ther and mother RCBCL) did not converge in the present study regarding an association between parents' and sons' childhood aggression. The single significant correlation between mothers' recollections of their own childhood behaviors and their sons' DSM-IV attention deficit dimensions suggests that inattention and hyperactivity-impulsivity may be transmitted exclusively and specifically from mothers to sons, as well as from fathers to sons. For mothers, as for fathers, childhood and were irrelevant to the prediction of sons' DSM-III oppositional, aggressive, and nonaggressive conduct dimensions. As was the case for the fathers' DSM data, this apparent discrepancy between the findings for maternal and corresponds to the findings of other DSM studies (Barkley et al., 1990; Biederman et al., 1986; Frick et al., 1991) concerning the divergent transmission of childhood hyperactivity and conduct disorder from fathers to sons. However, the sampling bias created by the exclusion of some of the most aggressive sons may also have attenuated the correlations between mothers' and sons' aggression. In contrast to the findings for fathers, there were no significant correlations between mothers' childhood symptoms and sons' scores on the two-factor measures or RCBCL factors. The correlations in this study suggest that family influences are partially involved in the transmission of childhood symptoms from parents to sons, but these correlations do not necessarily reflect the operation of genetic factors. Families in this study were living together, and the environmental effects on sons of their parents' persistent psychopathology may account for some of the relationship between the childhood symptoms of parents and sons. For example, parents who are still severely inattentive as adults may promote inattentive behaviors in their children by providing chaotic environments and treating their families in disorganized and inconsistent ways. Previous studies of this sample (Paternite et al., 1995, 1996) have noted the importance of the boys' comorbid or combined DSM disorders (attention deficit plus oppositional disorders, or the combined subtype of ADHD), as opposed to their pure DSM disorders (attention deficit or oppositional disorders alone, or the inattentive or hyperactive-impulsive ADHD subtypes alone) in accounting for impairment in the boys' functioning and behavior, including their RCBCL scores. In the present study, few parents rated themselves as high on both measures of childhood symptoms. The interaction of fathers' childhood inattention-hyperactivity and aggression (paternal comorbidity) accounted for significant variation in only two measures of their sons' behavior, and the interaction of mothers' childhood inattention-overactivity and aggression (maternal comorbidity) accounted for none. It is noteworthy that the only interactions in the present study were those involving DSM dimensions in sons. Although obtaining childhood information about fathers directly from them was intended to be a design improvement, it resulted here in 37% missing data for non-resident fathers. Boys who were excluded from the study because their biological fathers were not living with them were rated by their mothers as significantly more aggressive than boys who were living with both biological parents. Our empirical demonstration of this sampling bias is important, because such biases are not unique to the present study, but are pervasive in studies of disruptive child psychopathology. The present design, like designs that enroll nuclear families (e.g., Biederman et al., 1992), may underestimate aggressive childhood psychopathology in both sons and their biological fathers, while designs that include single-parent families and substitute the reports of the biological mothers for the selfreports of biological fathers may provide data of compromised reliability and validity. In order to provide the best estimates of paternal child psychopathology, future studies should obtain data directly from as many biological fathers as possible. When a proband's biological father cannot be found or will not participate, information should be sought from family members who knew the father as a child (e.g., the father's biological parents and older siblings) before resorting to information from family members who did not (e.g., the proband's biological mother). The present study was carried out primarily to test hypotheses about the transmission of childhood psychopathology from fathers and mothers to sons and not to validate the measures of the two-factor model. However, both the present analyses and the similar methods used to establish divergent validity can be seen as not providing sufficiently rigorous evidence that inattention-overactivity and aggression are separate dimensions. For instance, because the partial correlation between fathers' MBD-R and fathers' ratings of sons' RCBCL attention problems of.28 (p <.05) does not differ statistically from the partial correlation between fathers' MBD-R and fathers' ratings of sons' RCBCL attention problems of.14 (n.s.), the conclusion that fathers' is exclu-

10 508 Loney, Paternite, Schwartz, and Roberts sively correlated with sons' RCBCL attention problems can be viewed as tenuous. For these reasons, some investigators who have studied the inattention-overactivity and aggression dimensions (Atkins, Pelham, & Licht, 1989; Nolan & Gadow, 1994) have required what they call differential validity (two correlations must be significantly different) rather than divergent validity7 (one correlation is significant and the other is not). However, it is easy to present equally unsatisfying examples of the differential approach. For instance, in the present study, fathers' MBD-R would be considered an exclusive predictor of mothers' ratings of RCBCL attention problems (partial rs of for and.01 for are significantly different), but not an exclusive predictor of fathers' ratings of RCBCL attention problems (partial rs of.28 for and.14 for are not significantly different). Here a numerical, but not statistically significant, difference between nonsignificant correlations (.01 and.14) accounts for the discrepant conclusions. Another problem with the differential validity approach is demonstrated by the hypothetical pair of correlations.31 (p <.01) and.61 (p <.001). With n = 70, these correlations are significantly different from each other and would therefore indicate differential validity. However, because both coefficients are also statistically different from zero, they would not provide evidence for exclusive and specific transmission. A complete discussion is not possible here, but problems of this kind are inherent in conventional statistical significance testing where, in order to objectify decisionmaking, an arbitrarily placed line is considered to separate significance from nonsignificance. 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