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Spousal Associations for Alcohol Dependence and Educational
Attainment
Andrew WilliamsUniversity of North Carolina
Support from NIH Grants: AA07728, AA11998, AA13321, AA15210
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
Research Question
To what extent do assortative mating and social homogamy for educational attainment contribute to spousal concordance for alcohol dependence?
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
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
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 MZF 601 DZF 447 MZM 256 DZM
671 DZO
Marital StatusMarried (%) Separated/
Divorced/Widowed (%)
Never Married
All twins (n=6327) 76.7 9.8 13.6Twins with no spouse data (n=2655)
55.7 18.1 26.0
Twins with spouse interviewed (n=3672)
91.6 3.7 4.6
Spouses interviewed (n=3658)
98.2 1.5 0.4
Age and EthnicityMean Age at
1989 Questionnaire
Mean Age at 1996
InterviewFemale Twins 40.9 Male Partners 48.8Male Twins 39.4 Female
Partners44.0
Almost all respondents were of European ancestry
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
Frequency Percent
1 112 1.79
2 1743 27.79
3 1362 21.72
4 983 15.67
5 857 13.66
6 756 12.05
7 459 7.32
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
Education Level stratified by gender
Education Level Female (%) Male (%)
Low 26.86 15.87
Mid 56.17 56.02
High 16.97 28.11
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
MZF 0.82 0.47 0.56 0.53 0.56 0.50
MZM 0.79 0.52 0.46 0.44 0.55 0.42
DZF 0.63 0.32 0.49 0.30 0.29 0.26
DZM 0.54 0.56 0.60 0.37 0.44 0.15
DZO 0.52 0.41 0.49 0.44 0.40 0.24
c aeeca
A C E
1
maletwin
femalespouse
self-report
maletwin
self-report
E C A
maletwin
femalespouse
self-report
maletwin
self-report
MZ=1.0 DZ=0.5(1+μa2)
MZ and DZ =1.0
µ
1 11
wifewife
a=0.8705c=0.2492e=0.4256µ=0.5135
µ
Proportions of Variance a2 =0.76c2=0.06 e2=0.18
Assortative Mating Framework
c aee ca
A CE
1
maletwin
femalespouse
self-report
maletwin
self-report
EC A
maletwin
femalespouse
self-report
maletwin
self-report
1 11
wifewife
c
Cc
C
sssp ssp
m m
zw
a=0.5559c=0.6921e=0.4604m=0.9521z=0.9999w=0.0001
Proportions of Variancea2 =0.15(c+z)2=0.74e2=0.11
Social Homogamy Framework
Predicted Correlations from Assortative Mating Model
CorrelationTwin 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
MZF 0.82 0.51 0.51 0.42 0.42 0.22MZM 0.82 0.51 0.51 0.42 0.42 0.22DZF 0.59 0.51 0.51 0.30 0.30 0.16DZM 0.59 0.51 0.51 0.30 0.30 0.16DZO 0.59 0.51 0.51 0.30 0.30 0.16
Sex/Zygosity
MZF 0.82 0.47 0.56 0.53 0.56 0.50MZM 0.79 0.52 0.46 0.44 0.55 0.42DZF 0.63 0.32 0.49 0.30 0.29 0.26DZM 0.54 0.56 0.60 0.37 0.44 0.15DZO 0.52 0.41 0.49 0.44 0.40 0.24
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
MZF 0.79 0.46 0.46 0.46 0.46 0.44
MZM 0.79 0.46 0.46 0.46 0.46 0.44
DZF 0.63 0.46 0.46 0.46 0.46 0.44
DZM 0.63 0.46 0.46 0.46 0.46 0.44
DZO 0.63 0.46 0.46 0.46 0.46 0.44
Sex/Zygosity
MZF 0.82 0.47 0.56 0.53 0.56 0.50MZM 0.79 0.52 0.46 0.44 0.55 0.42DZF 0.63 0.32 0.49 0.30 0.29 0.26DZM 0.54 0.56 0.60 0.37 0.44 0.15DZO 0.52 0.41 0.49 0.44 0.40 0.24
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%
Alcohol Dependence Correlation Stratified by Education Level
Male
Low Mid High
FemaleLow 0.41 (n=288) 0.17 (n=586) 0.41 (n=95)
Mid 0.43 (n=253) 0.29 (n=1235) 0.15 (n=542)
High 0.58 (n=26) 0.13 (n=208) 0.38 (n=378)
Overall Correlation = 0.25
Bivariate Model – FemalesEducation
A C E
Alcohol Dependence
A ECorrelation
(95% CI)rG (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)
Bivariate Model – MalesEducation
A C E
Alcohol Dependence
A ECorrelation
(95% CI)rE (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)
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
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