2006 2004 1986 2000 2006 2004 2006 2005 2003 2002 2002 1996 2002 2006 2003 2005 2004 2003 2003 1998 1999 2004 2002 2006 2002 2006 2006 2005 2002 2003 1997 2002 2003 2005 2005 2006 2004 2006 1997 1998 2000 2006 2001 2006 1993 2002 2006 2000 2004 2002 Methods Participants 2000 2000 n n n n n n n n 1996 1 Table 1 n n  QLSCD 1 QLSCD 2  n % n % Sex of child      Male 1,123 51.2 884 50.7  Female 1,069 48.8 861 49.3 Age of mother at birth of first child      21 years or less 471 22.2 372 21.3  Older than 21 years 1648 77.8 1373 78.7 Mother graduated from high school      Yes 1865 84.0 1504 86.2  No 355 16.0 241 13.8 Family status      Two parents 1617 79.2 1407 80.6  One parent 424 20.8 338 19.4 Number of siblings in the home      None 830 40.6 713 40.9  One or more 1215 59.4 1032 59.1 Family income      Less than 30,000$ 639 29.3 468 26.8  30,000$–50,000$ 625 28.7 527 30.2  50,000$–80,000$ 611 28.0 499 28.6  More than 80,000$ 307 14.1 251 14.4 Data courtesy of the Institut de la Statistique du Québec Measurements Maternal prenatal smoking 2002 2005 1998 2004 2003 2002 2005 1998 2004 2003 2002 2003 2005 Huijbregts et al., 2006 2001 2002 Physical aggression and hyperactivity-impulsivity 1995 1987 1989 1987 2003 1999 2004 2004 2006 Control variables Potential confounders of associations between maternal prenatal smoking and early behavior problems were selected from four key domains: demographic factors (age at birth of first child, family status (separation/divorce: yes/no), presence of siblings, family income, maternal education); perinatal factors (alcohol and drug exposure during pregnancy, birth weight); family functioning and parenting (hostile reactive parenting, responsiveness, involvement), and parental background and mental health (mother’s and father’s history of antisocial behavior, maternal depression). Mothers provided information on most of these factors when their child was 5 months of age and again when their child was 17 months of age. 2006 2001 Parenting measures were obtained by observing the mother-child dyad during home visits at 5 and 17 months using the Home Observation for Measurement of the Environment (HOME)-Infant version (Caldwell & Bradley, 1984). The observations were carried out by trained observers who spent about 3 hours in the home to complete a battery of questionnaires and tests. These observers received a one-week training session and were closely supervised during the data collection. Three scales were obtained: hostile reactive parenting (e.g. “talks negatively about her child,” “shouts at her child,” “hits or physically punishes her child”; α=0.43 at 5 months and 0.73 at 17 months), responsiveness (e.g. “responds verbally to child’s vocalizations or verbalizations,” “tells child name of object or person during the visit,” “spontaneously praises the child at least twice”; α=0.85 at 5 months and 0.83 at 17 months), and involvement (e.g. “provides toys that challenge child to develop new skills,” “structures child’s play periods”; α=0.85 at 5 months and 0.88 at 17 months). Scores for each item on each scale ranged from 1 (never) to 5 (all the time). Only the scale score for hostile reactive parenting at 17 months was used because of the low internal reliability of this scale at 5 months. Mean scores across the 5 and 17 months assessments were used for the responsiveness and involvement scales. 1995 2000 2004 1981 1977 1995 2000 Huijbregts et al., 2006 2003 2004 2004 2004 2001 2006 2005 Data analyses Assignment to trajectories 1999 2005 2001 2005 2004 Prediction of physical aggression, hyperactivity/impulsivity, and their co-occurrence 2001 For the second set of analyses predicting PA and HI between ages 17 and 42 months, we contrasted, in weighted multinomial regression, those children who were high on both PA and HI (combined group), to those who were only high on PA (PA only group), to those only high on HI (HI only group) and to the remainder of the sample. Results Assignment to trajectories 1 2004 1 Fig. 1 *  Table 2 Maternal prenatal smoking and physical aggression (PA), hyperactivity-impulsivity (HI) and joint PA+HI trajectories between ages 17 and 42 months  MLE 1 (SE) MLE 2 (SE) MLE 3 (SE) χ 2 P Physical aggression −.40 (.09) −.24 (.07) NA 23.6 <.001 Physical aggression adjusted for control variables −.29 (.10) −.15 (.08) NA 8.4 .015 Hyperactivity −.56 (.15) −.41 (.11) −.22 (.11) 22.8 <.001 Hyperactivity adjusted for control variables −.32 (.17) −.24 (.13) −.13 (.13) 5.8 .121 Physical aggression and hyperactivity −.65 (.14) −.57 (.22) −.41 (.14) 31.2 <.001 Physical aggression and hyperactivity adjusted for control variables −.46 (.16) −.55 (.25) −.33 (.17) 10.5 .015 Note. 1999 2005 1 2004 2006 2006 2005 Physical aggression \documentclass[12pt]{minimal}
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\begin{document}$$\chi _{(6)}^2 = 114.5$$\end{document} p r p 3 3 4 Table 3 Co-occurrence of physical aggression (PA) and hyperactivity-impulsivity (HI) Probability of PA conditional on HI Sum  Low PA Moderate PA High PA   Low HI .40 .49 .11  1.0 Low-Moderate (L-M) HI .28 .54 .18  1.0 Moderate-High (M-H) HI .18 .49 .33  1.0 Chronic-High (C-H) HI .12 .39 .49  1.0 Probability of HI conditional on PA   Low HI L-M HI M-H HI C-H HI  Low PA .19 .51 .27 .03 1.0 Moderate PA .12 .48 .36 .04 1.0 High PA .05 .34 .50 .11 1.0 Joint probability of PA and HI   Low HI L-M HI M-H HI C-H HI Sum/PA Low PA .05 .13 .07 .01 .25 Moderate PA .06 .24 .18 .02 .51 High PA .01 .08 .12 .03 .24 Sum/HI .12 .45 .37 .06 1.0 Data courtesy of the Institut de la Statistique du Québec Table 4 Co-occurrence of physical aggression (PA) (2 levels) and hyperactivity-impulsivity (HI) (2 levels) Probability of PA conditional on HI Sum  Low PA High PA  Low HI .77 .23 1.0 High HI .51 .49 1.0 Probability of HI conditional on PA   Low HI High HI  Low PA .96 .04 1.0 High PA .89 .11 1.0 Joint probability of PA and HI  Low HI High HI Sum/PA Low PA .73 .03 .76 High PA .22 .03 .24 Sum/HI .95 .05 1.0 Data courtesy of the Institut de la Statistique du Québec \documentclass[12pt]{minimal}
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\begin{document}$$\chi _{(3)}^2 = 22.5$$\end{document} p Discussion The results of this study of early childhood show that maternal prenatal smoking was associated with PA but not with HI in covariate regression analyses when PA and HI were examined separately. When PA and HI were combined, a contrast between the PA-only group and the remainder of the sample, which was neither high on PA or HI, fell short of significance. However, maternal prenatal smoking predicted co-occurring elevated levels of PA and HI. Therefore the key finding of this study is that maternal prenatal smoking predicted high PA, but largely when it is co-occurring with high HI. Had we just examined PA and HI separately, as has often been done in studies of specificity, we would have missed the fact that HI is also sensitive to maternal prenatal smoking, even after controlling for several confounding variables, but only when it is combined with PA. 2001 2003 1999 2006 2000 1993 1996 2002 2004 1997 1998 2000 2004 2004 2006 2006 2006 2006 1994 2004 2006 2006 2003 1986 2000 2006 2005 2006 2004 2005 2006 2004 2005 2003 2002 2002 2004 2002 2001 2003 2005 2001 2003 2005 2006 2006 2005 2004 2001 2002 2005 2005 2004 2005 2006