Assessing the effect of regional deprivation on mortality avoiding compositional bias: a natural experiment

Background and objective We assessed the effect of regional
deprivation on individual mortality by making use of a natural
experiment: we followed up ethnic German resettlers from Former
Soviet Union countries who were quasi-randomly distributed across
the socioeconomically heterogeneous counties of Germany's federal
state North Rhine-Westphalia (NRW). Methods We used data from the
retrospective cohort study `AMOR' on the mortality of resettlers in
NRW (n=34 393). Based on the postcode of the last known residence
we linked study participants to the 54 counties of NRW, which were
aggregated in six deprivation clusters. Mortality rates and
standardised mortality ratios (SMRs) were calculated for each
cluster. After a mean follow-up of 10 years, 2580 resettlers were
deceased. Results For male and female cohort members, mortality
rates and SMRs were highest in the cluster `poverty poles' (SMR
men: 1.21, 95% CI 1.04 to 1.41; SMR women: 1.17, 95% CI 0.99 to
1.37), whereas they were lowest in the cluster `prospering regions
and suburban counties' (SMR women: 0.86, 95% CI 0.70 to 1.05) as
well as in the cluster `heterogeneous counties' (SMR men: 0.73, 95%
CI 0.61 to 0.88). Conclusions The population which was
quasi-randomly distributed to counties of differing socioeconomic
status experienced different levels of mortality. It was highest in
regions with the highest level of regional deprivation. Previous
studies describing this positive relationship between mortality and
regional deprivation could not differentiate between compositional
and contextual effects. Thus, our findings indicate that in terms
of mortality, regional deprivation does matter.