Incidence of disability pension and associations with socio-demographic factors in a Swedish twin cohort

The incidence of disability pension (DP), especially due to mental diagnoses, has increased in many countries, but knowledge
of socio-demographic risk factors for DP is limited. Further, the influences of genetics and early-life factors (jointly called
familial factors) on these associations remain to be studied. The aims were to study incidence of DP (due to all and mental
diagnoses) and associations with socio-demographic factors, and also to establish whether associations differ with DP diagnosis
and sex, and are influenced by familial factors.

A prospective cohort study of all twins born in 1928–1958 (n = 52,609) in Sweden was conducted. The twins were followed from 1993 to 2008 regarding DP. Cox proportional hazard models
were applied.

The cumulative incidence of DP was 17 %. Of all the DP diagnoses 20 % were mental. Higher age (≥45 years), being a woman or
unmarried, and/or living in a semi-urban area were risk factors for DP. Low education, being a blue-collar worker or being
self-employed predicted either higher (all diagnoses) or lower (mental diagnoses) risk of DP. Rural areas were associated
with DP due to mental diagnoses. The estimates varied for men and women. After adjustment for familial factors the associations
of DP with education and marital status were attenuated and no longer significant. Similar results were apparent for DP due
to mental diagnoses and socioeconomic status.

Familial factors may select individuals into some of the established risk environments for DP. Studies investigating the causes
of DP need to take such confounding into account.