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Social Inequality in Health – Causation and Selection: A Twin Approach

Social Inequality in Health – Causation and Selection: A Twin Approach. Ph.D. Student Mia Madsen DARC: Odense & Copenhagen, Project start June 2008 Supervisors Kaare Christensen, Merete Osler, Anne-Marie Nybo Andersen. Research question.

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Social Inequality in Health – Causation and Selection: A Twin Approach

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  1. Social Inequality in Health – Causation and Selection: A Twin Approach Ph.D. Student Mia Madsen DARC: Odense & Copenhagen, Project start June 2008 Supervisors Kaare Christensen, Merete Osler, Anne-Marie Nybo Andersen

  2. Research question • A strong and consistent association between socioeconomic position and health is well-established, but is this association a true causal relationship or a spurious one, produced by underlying background factors?

  3. Analytical approachCausation or selection? Genetics Matched on genotype (partly or fully) and childhood environment Selection Childhood environment Do they differ significantly with respect to health outcomes? Discordant on adult SEP ? Health SEP Causality

  4. The principal of twin studies: Three comparisons

  5. The evidence so far… • Contradictory findings • Generally, no association between SEP and health when genetic constitution and rearing environment are controlled for. Osler et al. 2007, Osler et al. 2009 & Behrman et al. (work in progress) (Danish data) • Persisting association between SEP and health in intra-pair analyses (Krieger et al. 2005 & Lundborg 2008) (American data)

  6. Social Science and Medicine, 2009

  7. Evidence continued… • Societal context seems to play a role • Results seem to depend on the social indicators used • Results seem to vary according to health outcomes studied • Power limitations? • Chance findings?

  8. Editorial IJE • ”...These are important findings that now require replication in larger twin data sets using a wider range of health outcomes…” (Ebrahim, S) • Aim: In nation-wide registers to investigate the effect of different social indicators during the life course on survival and a wide range of different health outcomes in a twin population matched on early life experiences and genetic make-up (partly or fully)

  9. Danish Twin Registry (1870 and onwards, N=75,000+) Statistics Denmark (Information on all twins + 5% sample of all birth cohorts from the general population) Health Causes of death (1973-2006) Hospitalizations (incl. diagnoses, operations, and accidents causing admission to hospital (1977-2004)) Cancer registry (soon) Data sources & information • Social data • Income (1980-2004) • Occupation (1980-2004) • Socio-economic position (1980-2004) • Civil status (1980-2004) • Education (1980-2004)

  10. 1st paper – initial analyses • Educational status and all cause and cause-specific mortality • Follow-up: 1980-2006 • Education: 1980, International Standard of Classification (ISCED) (Primary/Secondary, Upper secondary/Post-secondary non-tertiary, Tertiary) • Mortality: All cause, CVD (+ischemic and stroke), Cancer, Smoking-related cancer, Respiratory causes, External causes, Abnormal findings/insufficiently defined symptoms

  11. Study population

  12. Descriptives, education • Discordant twin pairs • Primary/secondary & Post-secondary: N=6000 (900 MZ) • Primary/secondary & Tertiary: N=3060 (402 MZ) • Post-secondary & Tertiary: N=1456 (198 MZ)

  13. Educational status and selected causes of deathCox regression analysis

  14. Summary of results • The effect of education seems to persist in the intrapair analyses for all cause mortality and CVD. For cancer the pattern is less clear. • Results are compatible with an independent effect of educational status in adulthood above and beyond genetic constitution and other background factors.

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