Author(s): Amir Baigi, Anders Holmén
Introduction: Migration is an important factor that could influence the distribution of disease and death in a population. The majority of studies on migration and health relate to external migration i.e. between different countries and cultures and has been thoroughly investigated in various settings. Studies of health effects related to internal migration, i.e. within the borders of a country however, are much rarer.
Aim: The aim of the current study was therefore to examine, from a socio-epidemiological perspective, the impact of internal migration on the risk of death from different diseases among individuals born in a province in south-west Sweden, living in the province itself or in other parts of the country. Material and methods: The study comprised the whole population of both Sweden and the province of Halland and had a historical, prospective design which made it possible to follow individuals from 1980 to 1990. The participants were aged between 25 and 55 years in 1980 when the individual background variables were collected for the first of three times by repeated Swedish national questionnaires i.e. the Population and housing census (FoB). All deaths listed in the international classification of diseases (ICD) during the 10-year period from 1980-1990 were included.
Statistical methods: The risk of death was estimated by Poisson regression as a function of age, marital status, educational level and socio-economic classification (SEI) for Sweden as a whole. The expected number of deaths was calculated by taking all of the abovementioned variables into account. For the hazard rate (HR), 95% confidence intervals were calculated. Comparisons between the observed and expected number of deaths were performed by means of Poisson distribution.
Results: Men born in Halland and still living there had a lower risk of death than other male residents of the province who were born elsewhere (HR 0.89 CI 0.80–0.99). Women showed a similar, although non-significant tendency. The results also revealed that those natives of Halland who had moved to another part of the country retained their advantage compared to Swedes born outside the province and living in other parts of Sweden. This difference was statistically significant among men (HR 0.90 CI 0.81–0.99) while a non-significant tendency in the same direction was seen in women. All these comparisons were adjusted for the background variables as age, marital status, educational level and SEI.
