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Familial Influences on Substance Use by Adolescents and Young Adults Author(syf 0 L F K D H O + % R \ O H 0 D U N 6 D Q I R U G 3 H W H U 6 ] D W P D U L . D W K O H H Q 0 H U L N D Q J D V D Q d David R. Offord Source: Canadian Journal of Public Health / Revue Canadienne de Santé Publique, Vol. 92, No. 3 (MAY / JUNE 2001yf S S 9 Published by: Canadian Public Health Association Stable URL: http://www.jstor.org/stable/41993309 Accessed: 03-08-2017 05:40 UTC REFERENCES Linked references are available on JSTOR for this article: http://www.jstor.org/stable/41993309?seq=1&cid=pdf-reference#references_tab_contents You may need to log in to JSTOR to access the linked references. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://about.jstor.org/terms Canadian Public Health Association is collaborating with JSTOR to digitize, preserve and extend access to Canadian Journal of Public Health / Revue Canadienne de Santé Publique This content downloaded from 208.95.50.183 on Thu, 03 Aug 2017 05:40:06 UTC All use subject to http://about.jstor.org/terms Familial Influences on Substance Use by Adolescents and Young Adults Michael H. Boyle , PhD,1 Mark Sanford, MB ChB,1 Peter Szatmari , MD,1 Kathleen Merikangas, PhD,2 David R. Offord, MD1 Substance use by adolescents and young adults is increasing after a decade-long decline in use during the 1980s.1"4 Efforts to understand factors leading to drug use in this age group have focused on genetic, individual and environmental influences (especially family, peer and school environ- mental factorsyf ( Y L G H Q F H V X J J H V W V W K D t genetic factors account for a large share of observed familial aggregation of use and abuse of alcohol and illicit drugs, and that both general and drug-specific genetic influences are at play.6 However, the rela- tive importance of environmental and genetic factors is unclear. For example, a recent population-based twins study found little evidence of family environmental fac- tors causing alcohol-related disorders in contrast to earlier clinic- and court-based studies.7 In contrast, in a U.S. adoption cohort, substantial environmental effects were reported for sibling aggregation (but not for parent-child aggregationyf R I D O F R - hol use and problem drinking (r = 0.24 in non-biological siblings, r = 0.45 in same sex/same age siblings vs. r = 0.01 (p>0.05yf for opposite sex/dissimilar age siblingsyf 8 A criticism of the literature in this area is that very few studies have used representa- tive community-based samples to evaluate these issues free from the referral biases 1. Department of Psychiatry and Behavioural Neuroscience and Centre for Studies of Children at Risk, McMaster University, Hamilton, ON 2. Departments of Psychiatry and Epidemiology, Yale University, New Haven, CT Correspondence and reprint requests: Michael H. Boyle, Centre for Studies of Children at Risk, McMaster University Faculty of Health Sciences and Hamilton Health Sciences Corporation, Patterson Building, Chedoke Division, Hamilton Health Sciences Corporation, Box 2000, Hamilton, ON, L8N 3Z5, Tel: 905-521-2100 ext 77365, E-mail: [email protected] Dr. Michael Boyle is supported by a Canadian Institutes of Health Research Scientist Award and Dr. Peter Szatmari is supported by a Senior Fellowship Award from the Ontario Mental Health Foundation. inherent in clinic samples.9 Two such stud- ies report on sibling effects. In the U.S. National Survey on Drug Abuse, drug use by teenagers correlated with drug use by fathers (from r = 0.17 for current cigarette use to r = 0.31 current marijuana useyf E y mothers (from r = 0.04 (p>0.05yf I R U F X U U H Q t alcohol use to r = 0.30 for lifetime mari- juana useyf D Q G E \ R O G H U V L E O L Q J V U 7 (p>0.05yf I R U O L I H W L P H F R F D L Q H X V H W o r = 0.30 for lifetime marijuana useyf , Q a second study, alcohol use was highly con- cordant among spouses (r = 0.67yf E X W O H V s so among parents and offspring and sib- lings (from r = 0.25 to r = 0.44yf 1 The objective of this study is to examine family influences on tobacco, alcohol, and marijuana use by 12-24 year olds in a rep- resentative general population sample liv- ing at home. The following questions are addressed: 1yf Z K D W L V W K H S U H Y D O H Q F H R I V X E - stance use among family members?; 2yf G R H V V L E V K L S V W U X F W X U H L Q I O X H Q F H D J J U H J D - tion or clustering of substance use in fami- lies?; 3yf G R H V J H Q G H U R U D J H L Q I O X H Q F e within-family correlations of substance use?; and 4yf L V V X E V W D Q F H X V H D P R Q J \ R X Q J H U V L E - lings associated more strongly with parental substance use or substance use by older siblings? Answers to these questions will provide insight into the relative importance of parental and sibling effects and whether observed sibling aggregation is likely to be due to shared genetic or environmental effects. METHODS Survey design Information for this research comes from the Ontario Health Survey (OHS: ref. 12yf 7 K H V D P S O H Z D V R E W D L Q H G X V L Q J a stratified multi-stage cluster design: there were 35,479 dwellings selected and 87.5yb of these yielded a person knowledgeable 206 REVUE CANADIENNE DE SANTÉ PUBLIQUE VOLUME 92, NO. 3 ABSTRACT This study uses data from the Ontario Health Survey to examine within-family influences (sibship number, age and sex com- position; family structure and parental sub- stance useyf R Q W K H X V H R I W R E D F F R D O F R K R l and marijuana in households (N=4,643yf among offspring aged 12 to 24 years. Using a modification of the kappa statistic, concor- dance among siblings is modest generally and undifferentiated across substance type. Concordance is stronger among sibships that are either all male or older (19-24 yearsyf D Q d is particularly strong for siblings < two years apart in age. The dominant influence of sub- stance use behaviour appears to be from older siblings to younger siblings and not from parents to offspring. Sibling concor- dance for substance use suggests that the treatment and prevention of substance use (and abuseyf D P R Q J D G R O H V F H Q W V D Q G \ R X Q g adults might be enhanced by including a family focus, especially where there are two or more siblings at home. ABRÉGÉ L'étude, fondée sur les données de l'Enquête sur la santé en Ontario, porte sur les influences intrafamiliales (nombre, âge et sexe des mem- bres de la fratrie, structure familiale et consom- mation de drogues par les parentsyf V X U O D F R Q - sommation de tabac, d'alcool et de marijuana dans des familles (n = 4 643yf G D X P R L Q V X n parent et un enfant de 12 à 24 ans. Une analyse Kappa modifiée révèle une concordance frater- nelle modeste dans l'ensemble, peu tranchée selon le type de drogue. La concordance est plus prononcée lorsque la fratrie se compose unique- ment de garçons ou comporte un membre plus âgé (19 à 24 ansyf S D U W L F X O L U H P H Q W O R U V T X e l'écart entre les membres est de deux ans ou moins. L'influence dominante, en matière de consommation de drogues, semble s'exercer des aînés aux cadets et non des parents aux enfants. La concordance constatée entre les membres de fratries porte à croire que l'on pourrait améliorer le traitement et la prévention de la consomma- tion (et de l'abusyf G H G U R J X H V F K H ] O H V D G R O H V - cents et les jeunes adultes en y intégrant une composante familiale, surtout lorsqu'il y a plus d'un enfant à la maison. This content downloaded from 208.95.50.183 on Thu, 03 Aug 2017 05:40:06 UTC All use subject to http://about.jstor.org/terms MAY - JUNE 2001 CANADIAN JOURNAL OF PUBLIC HEALTH 207 about the household who agreed to pro- vide information on sociodemographic and general health variables of all residents in a personal interview. Self-administered ques- tionnaires on more personal health issues (including substance useyf Z H U H O H I W I R r completion by all household members aged 12 years and older. Sample for analysis The sample consisted of families with at least one offspring aged 12 to 24 years and at least one natural parent in the home. All household members other than offspring and their natural parent(syf Z H U H H [ F O X G H G . Applying these criteria yielded a potential sample of 23,915 individuals living in 6,976 families. Failure of individuals to return self-administered questionnaires reduced the sample by 24.5yb (5,861/23,915yf 0 L V V L Q J G D W D R Q R Q H R r more of the variables needed for the analy- ses reduced the sample by another 14.9yb (3,564/23,915yf $ F R P S D U L V R Q R I U H V S R Q - dents and nonrespondents based on inter- view data is presented in Table I. Most dif- ferences are less than 5yb D Q G Q R Q H D U e larger than 10yb 7 K H I R O O R Z L Q J J U R X S s (>5yb G L I I H U H Q F H V \f may be over-represented: one-parent households; parents born in Canada who were younger and better edu- cated; and siblings who were older and female. Variables and measures The substance use variables were mea- sured independently for respondents based on their answers to self-administered ques- tionnaires. Use of cigarettes refers to daily consumption; use of alcohol refers to aver- age weekly consumption of 2 or more drinks in the previous 12 months; use of marijuana refers to lifetime use of marijua- na, cannabis or hash at least 5 times. Sociodemographic variables were derived from responses provided by the knowl- edgeable household member to the interviewer-administered questionnaire. Analysis Prevalences are estimated by the number of users per 100 for each category of sub- stance use. A modification of the kappa statistic proposed by Fleiss13 is used to esti- mate familial aggregation. In this method, TABLE I Distribution of Selected Characteristics of Respondents and Nonrespondents Characteristics Respondents Nonrespondents Households (6976yf \f (2333yf Urban residence 74.5 70.2 <6 members in household 93.4 91.8 Income below the poverty line 1 4.4 11 .0 One parent in home 1 8.3 1 3.0 Parents (12,919yf \f (5170yf Female 54.1 49.7 Age in years <50 78.4 71 .2 Birthplace Canada 75.5 66.6 Secondary school complete 64.1 58.2 Working 79.1 79.1 Siblings (1 0,996yf \f (4255yf Female 49.2 42.2 Age in years 1 8-24 61 .1 54.6 In school 83.0 78.2 TABLE II Substance Use Prevalence per 100 Among Parents and Siblings Tobacco Alcohol Marijuana (currentyf R Q H \ H D U \f (lifetimeyf Parents Mothers (4194yf 5 Fathers (3555yf 5 Siblings Sex Females (3423yf 6 Males (3318yf 7 Age in years 12-14(2073yf 3 15-17(2048yf 9 18-20(1580yf 3 21-24(1040yf 0 TABLE III Family Composition and Aggregation of Substance Use Among Siblings Feature Category (nyf 7 R E D F F R $ O F R K R O 0 D U L M X D Q a Overall (1 727yf \f 0.1 5 (0.02yf \f Number of siblings 2 (1 405yf \f 0.1 4 (0.03yf \f >3 (322yf \f 0.1 8 (0.03yf \f Sex composition All female (368yf \f 0.09 (0.05yf \f All male (41 5yf \f 0.1 7 (0.04yf \f Mixed (994yf \f 0.1 4 (0.03yf \f Age composition All 1 2-1 8 (971 yf \f 0.1 6 (0.03yf \f All 1 9-24 (1 82yf \f 0.25 (0.06yf \f Mixed (574yf \f 0.03 (0.03yf \f * not significant at p<0.05 an analysis of variance approach is taken to adjust for variations in the number of sib- lings per family. Absolute differences between kappas in excess of 0.10 are defined arbitrarily as 'important' effects. Considered in this analysis are the effects of sibship structure (sibship size, sex com- position and age compositionyf R Q I D P L O L D l aggregation. Kappa is used also to examine the effects of gender and age on within- family correlations by estimating levels of concordance on substance use between pairs of family members, including spous- es, spouses and siblings and siblings sub- divided by sex and age. Households with four or more siblings [43/4,643 (0.9yb \f] are excluded from this analysis to prevent large sibships from exerting undue weight on the analysis. Finally, logistic regression analysis is used to estimate the strength of This content downloaded from 208.95.50.183 on Thu, 03 Aug 2017 05:40:06 UTC All use subject to http://about.jstor.org/terms FAMILIAL INFLUENCES TABLE IV Kappa Estimates of Agreement Between Family Members on Substance Use Members (nyf 7 R E D F F R $ O F R K R O 0 D U L M X D Q a Spouses (3106yf \f 0.32(0.02yf \f Father-Son (2728yf \f 0.09(0.02yf \f Father-Daughter (2492yf \f 0.06(0.01yf \f Mother-Son (3106yf \f 0.07(0.02yf \f* Mother-Daughter (301 7yf \f 0.12(0.02yf \f Brothers < 2 yrs (290yf \f 0.44 (0.07yf \f Brothers > 2 yrs (333yf \f* 0.07 (0.04yf \f* Sisters < 2 yrs (240yf \f 0.34(0.11yf \f Sisters > 2 yrs (284yf \f* 0.05(0.06yf \f Brothers-Sisters <2 yrs (51 6yf \f 0.22(0.06yf \f Brothers-Sisters > 2 yrs (579yf \f 0.1 1 (0.04yf \f * not significant at p<0.05 TABLE V Strength of Association Estimated by Relative Odds and 95yb & R Q I L G H Q F e Intervals in Logistic Regression Between Substance Use in Youngest Sibling Characteristic Tobacco Alcohol Marijuana Youngest sibling Male gender 1 .46 (0.99-2.14yf W \f 1 .42 (0.93-2.1 7yf Age in years 1 .37t (1 .28-1 .47yf W \f 1 .46f (1 .35-1 .59yf Parents Lone parent 1 .36 (0.91 -2.04yf \f 1 .24 (0.79-1 .96yf Substance used 1 .37 (0.93-2.03yf \f 1 .91 (0.96-3.80yf Siblings >2 in home 0.63 (0.36-1 .11yf \f 0.78 (0.43-1 .42yf Substance used 4.08t (2.75-6.05yf I \f 5.34t (3.48-8.1 8yf t p<0.001 association between substance use by the youngest sibling in the family (dependent variableyf D Q G X V H R I W K H V D P H V X E V W D Q F H E y parent(syf D Q G R O G H U V L E O L Q J V \f. RESULTS Prevalences and sibship structure Prevalences for all substances used are higher among fathers than among mothers and among male siblings than among female siblings (Table IIyf $ P R Q J V L E O L Q J V , there is a gradient of increasing substance use by age that begins to taper off among 21-24 year olds. Table III shows that overall levels of aggregation are modest for use of tobacco, alcohol and marijuana (k=0.19, 0.15, 0.20yf ( V W L P D W H V R I D J J U H J D W L R Q H [ K L E L t small variation by sibship size. Sibships composed entirely of males versus females exhibit higher levels of aggregation for use of tobacco (k=0.2 4 versus 0.09yf D Q G P D U L - juana (k=0.28 versus 0.17yf $ J H F R P S R V L - tion exerts the most potent effect on esti- mates of aggregation: sibships composed entirely of young adults aged 19 to 24 years show the highest levels of aggregation for all categories of substance use. Within family correlations Concordance for the same categories of substance use are much higher between parents (k=0.30 to 0.44yf W K D Q E H W Z H H Q S D U - ents and their children (k=0.05 to 0.16yf (Table IVyf 7 K H U H D S S H D U V W R E H D V P D O l gender-specific effect for tobacco use. Concordance between father-son and mother-daughter are 0.14 and 0.16, respec- tively; between father-daughter and mother- son, they are 0.04 and 0.06, respectively. Concordance on substance use between siblings are influenced by both closeness in age and sex. Siblings more than two years apart in age exhibit low concordance on substance use for all pairings (k=0.02 to 0.14yf 6 L E O L Q J V Z L W K L Q W Z R \ H D U V R I H D F h other exhibit higher levels of concordance: these estimates are higher for brother (k=0.33 to 0.45yf W K D Q I R U V L V W H U N W o 0.34yf D Q G E U R W K H U V L V W H U S D L U L Q J V N 3 to 0.28yf 7 D E O H , 9 \f. Parent and older sibling substance use Table V presents relative odds (ROyf between substance use reported by parents and older siblings and substance use reported by the youngest member of the sibship. Covariates are included to control for family status (one vs. two parentsyf V L E - ship size (3 or more vs. 2yf D Q G W K H D J H D Q d gender of the youngest sibling. The strength of association between parental substance use and use of the same sub- stance by the youngest sibling is small and nonsignificant (R0=1.09 to 1.91yf 7 K H V e contrast with substance use by older sib- lings which is associated strongly and sig- nificantly with substance use by younger siblings (RO=3.77 to 5.34yf . DISCUSSION This study provides evidence for the aggregation of substance use among sib- lings in families. Overall, the effect is mod- est, appears to be undifferentiated across substance type and is stronger among sib- ships that are either all male or older (19- 24 yearsyf : L W K L Q I D P L O \ F R Q F R U G D Q F H L s particularly strong for spouses and for sib- lings < two years apart in age. Furthermore, the dominant influence of substance use behaviour appears to be from older siblings to younger siblings and not from parents to offspring. There are a number of possible explana- tions for the strong between-sibling associ- ations in substance use observed in this study. First of all, access to tobacco, alco- hol and drugs such as marijuana is deter- mined very much by age. The presence of older siblings already engaging in sub- stance use provides the means for younger siblings to obtain these substances. Second, older siblings constitute important role models, and in some instances the initia- tion of younger siblings into substance use may arise from imitative behaviour. Third, closeness in age will have important influ- ences on socialization processes. Siblings close in age can be expected to spend more time together through childhood and ado- lescence. This will lead to more shared experiences in the family, neighbourhood, at school and with adolescent peer groups. An older sibling engaging in substance use will likely have peers engaged in the same 208 REVUE CANADIENNE DE SANTÉ PUBLIQUE VOLUME 92, NO. 3 This content downloaded from 208.95.50.183 on Thu, 03 Aug 2017 05:40:06 UTC All use subject to http://about.jstor.org/terms activity who, in turn, could serve as impor- tant role models for engaging in substance use and provide additional opportunities to access tobacco, alcohol and marijuana. The relatively weak associations between parental substance use and substance use by younger siblings should not be inter- preted to mean that parental behaviour has no impact on substance use in the family. In addition to substance use behaviour, there are other within-family processes such as afFectional ties, management prac- tices and the resolution of conflict that may have important implications for sub- stance use among siblings.14 Study limitations There are a number of study limitations that the reader should bear in mind when considering the findings. One, all informa- tion was collected by self-administered questionnaire completed at home, without opportunity to corroborate responses. Although studies exist in support of the reliability and validity of this method,15 it is arguable that random error and under- reporting have led to an attenuation of associations. Two, the statistic used to measure concordance on substance use - kappa - is compressed downward by low base rates.16 Three, although respondents and nonrespondents are comparable on sociodemographic characteristics, net data loss at 39.4yb L V K L J K D Q G F R X O G L Q F O X G e sample loss selective for substance use. Four, it is not possible to establish the chronology of substance use within fami- lies because the study design is cross- sectional. Five, data are not available on intensity of contact between siblings or peer substance use, variables that would help to clarify the modifying effects of age on between-sibling agreement in substance use. And six, the study is restricted to the effects of family composition on substance use. There is no attempt to determine whether or not the socioeconomic circum- stances of families act as effect moderators or to model the impact of other important influences on substance use such as family processes and peers. Identification of risk factors associated with substance use by adolescents and young adults is important from both pre- ventive and therapeutic viewpoints. Sibling concordance for substance use points to the importance of environmental effects and suggests that the treatment and pre- vention of substance use (and abuseyf among adolescents and young adults might be enhanced by including a family focus, especially where there are two or more sib- lings at home. Empirical support exists for family-based treatments for substance abuse and family-based preventive inter- ventions are under development.17 Evaluation of the effectiveness of these pre- ventive programs should be a priority for research on interventions. REFERENCES 1. Adlaf EM, Ivis EJ, Smart RG, Walsh GW. The Ontario Student Drug Use Survey: 1977-1995. Toronto: Addiction Research Foundation of Ontario, 1995. 2. Adlaf EM, Ivis FJ, Smart RG, Walsh GW. Enduring resurgence or statistical blip? 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