1. Spousal Associations for Alcohol Dependence and Educational Attainment Andrew Williams University of North Carolina Support from NIH Grants: AA07728, AA11998, AA13321, AA15210

2. Introduction Substance abuse associated with low educational attainment This association could be linked to familial determinants (genetic and/or environmental) – Likely correlated between spouses – Such factors are of interest because they may lead to an increase in prevalence of alcohol dependence Grant et al., 2007

3. Research Question To what extent do assortative mating and social homogamy for educational attainment contribute to spousal concordance for alcohol dependence?

4. Background – Assortative Mating A process of non-random mating in which individuals select spouses based on characteristics that they and their partner share – “like marries like” – positive AM – “opposites attract” – negative AM Over time, this can lead to a relative increase in the proportion of variability attributable to genetic factors Grant et al., 2007

5. Background – Social Homogamy A social process in which similarities in spouses stem from their correlated environments Passive influence on mate selection Grant et al., 2007

6. Sample Information 6327 individuals from the “1981 cohort” of the Australian Twin Study completed a mailed questionnaire in 1989 – 2995 complete pairs and 337 individuals from twin pairs – 3669 spouses (1356 wives, 2313 husbands) completed a telephone diagnostic interview between 1994-1997 1020 MZF601 DZF 447 MZM256 DZM 671 DZO

7. Hansell et al., 2008

8. Marital Status Married (%)Separated/Divorc ed/Widowed (%) Never Married All twins (n=6327) 76.79.813.6 Twins with no spouse data (n=2655) 55.718.126.0 Twins with spouse interviewed (n=3672) 91.63.74.6 Spouses interviewed (n=3658) 98.21.50.4

9. Age and Ethnicity Mean Age at 1989 Questionnaire Mean Age at 1996 Interview Female Twins40.9Male Partners48.8 Male Twins39.4Female Partners 44.0 Almost all respondents were of European ancestry

10. Educational Attainment Variable 1 = 7 or fewer years of school 2 = 8-10 years 3 = 11-12 years 4 = Apprenticeship or diploma 5 = Technical or teachers’ college 6 = University first degree 7 = University post- graduate degree Education level FrequencyPercent 11121.79 2174327.79 3136221.72 498315.67 585713.66 675612.05 74597.32

11. Educational Attainment Variable 1 = 7 or fewer years of school 2 = 8-10 years 3 = 11-12 years 4 = Apprenticeship or diploma 5 = Technical or teachers’ college 6 = University first degree 7 = University post-graduate degree Low Mid High

12. Education Level stratified by gender Education LevelFemale (%)Male (%) Low26.8615.87 Mid56.1756.02 High16.9728.11

13. Observed Polychoric Correlations for Educational Attainment Correlation Twin A x Twin B Twin A x Spouse A Twin B x Spouse B Twin A x Spouse B Twin B x Spouse A Spouse A x Spouse B Sex/ Zygosity MZF0.820.470.560.530.560.50 MZM0.790.520.460.440.550.42 DZF0.630.320.490.300.290.26 DZM0.540.560.600.370.440.15 DZO0.520.410.490.440.400.24

14. caeeca ACE 1 male twin female spouse self-report male twin self-report ECA male twin female spouse self-report male twin self-report MZ=1.0 DZ=0.5(1+ μ a 2 ) MZ and DZ =1.0 µ 111 wife a=0.8705 c=0.2492 e=0.4256 µ=0.5135 µ Proportions of Variance a 2 =0.76 c 2 =0.06 e 2 =0.18 Assortative Mating Framework

15. caeeca ACE 1 male twin female spouse self-report male twin self-report ECA male twin female spouse self-report male twin self-report 111 wife c C c C ss sp mm z w a=0.5559 c=0.6921 e=0.4604 m=0.9521 z=0.9999 w=0.0001 Proportions of Variance a 2 =0.15 (c+z) 2 =0.74 e 2 =0.11 Social Homogamy Framework

16. Predicted Correlations from Assortative Mating Model Correlation Twin A x Twin B Twin A x Spouse A Twin B x Spouse B Twin A x Spouse B Twin B x Spouse A Spouse A x Spouse B Sex/ Zygosity MZF0.820.51 0.42 0.22 MZM0.820.51 0.42 0.22 DZF0.590.51 0.30 0.16 DZM0.590.51 0.30 0.16 DZO0.590.51 0.30 0.16 Sex/ Zygosity MZF0.820.470.560.530.560.50 MZM0.790.520.460.440.550.42 DZF0.630.320.490.300.290.26 DZM0.540.560.600.370.440.15 DZO0.520.410.490.440.400.24

17. Predicted Correlations from Social Homogamy Model Correlation Twin A x Twin B Twin A x Spouse A Twin B x Spouse B Twin A x Spouse B Twin B x Spouse A Spouse A x Spouse B Sex/ Zygosity MZF0.790.46 0.44 MZM0.790.46 0.44 DZF0.630.46 0.44 DZM0.630.46 0.44 DZO0.630.46 0.44 Sex/ Zygosity MZF0.820.470.560.530.560.50 MZM0.790.520.460.440.550.42 DZF0.630.320.490.300.290.26 DZM0.540.560.600.370.440.15 DZO0.520.410.490.440.400.24

18. Alcohol Dependence Variable Approximated DSM-IV (no clustering with 12- month period) Prevalences: – Female twins – 4% – Male twins – 18% – Female spouses – 8% – Male spouses – 23%

19. Alcohol Dependence Correlation Stratified by Education Level Male LowMidHigh Female Low0.41 (n=288)0.17 (n=586)0.41 (n=95) Mid0.43 (n=253)0.29 (n=1235)0.15 (n=542) High0.58 (n=26)0.13 (n=208)0.38 (n=378) Overall Correlation = 0.25

20. Bivariate Model – Females Correlation (95% CI) r G (additive genetic)0.27* (0.08 to 0.50) * Indicates p<0.05 0.19* (0.16-0.22) 0.30* (0.17-0.46) 0.51* (0.38-0.58) 0.63* (0.52-0.78) 0.37* (0.22-0.53)

21. Bivariate Model – Males Correlation (95% CI) r E (nonshared environmental)-0.37* (-0.53 to -0.21) * Indicates p<0.05 0.21* (0.17-0.27) 0.21* (0.11-0.32) 0.58* (0.43-0.70) 0.54* (0.54-0.71) 0.46* (0.29-0.58)

22. Conclusions Evidence of spousal correlation for educational attainment and alcohol dependence Educational attainment – cannot distinguish between the contributions of AM and SH, but both may make significant contributions Bivariate genetic models in twins showed modest evidence of genetic overlap for females and nonshared environment for males

23. Future Work Further refinement of social processes for educational attainment is needed – A better approach may be to stratify by education levels and nest assortative mating for alcohol dependence Larger samples are needed to test suggestive associations in this sample

24. Acknowledgements Arpana Agrawal, Ph.D. Kathleen K. Bucholz, Ph.D. Julia D. Grant, Ph.D. Andrew C. Heath, D.Phil. Michael T. Lynskey, Ph.D. Pamela A.F. Madden, Ph.D. John B. Whitfield, Ph.D. Nicholas G. Martin, Ph.D.