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

Hansell et al., 2008

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

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.