Clemens T, Boyle P, Popham F. Unemployment, mortality and the problem of health-related selection: evidence from the Scottish and England and Wales (ONS) Longitudinal Studies. Health Statistics Quarterly 2009; 43 (Autumn): 7-13.
Testing whether unemployment causes health deterioration is complicated because failing health may increase the probability of unemployment. In some previous studies of unemployment and mortality a ‘wear-off’ period is used to exclude any deaths occurring in the first few years after employment status was observed. It is assumed that selection effects will wear-off during this period. In this article the effectiveness of using wear-off periods is tested. Using data from the Scottish
Longitudinal Study and the England and Wales Longitudinal Study, logistic regression models were used for estimating the odds of death in a given time period after the 1991 Census for
those aged 35–64 in 1991. The odds ratios for the different economic positions (in work, unemployed, retired, permanently sick and other inactive) were compared, as well as the changes in risk associated with cumulatively increasing the length of
wear-off prior to follow-up. No evidence was found of healthrelated
selection for the unemployed in 1991. This observation was consistent across both studies. This suggests that the use of the five year wear-off period in many studies of mortality and unemployment may be an ineffective and unnecessary technique for mitigating the effects of health-related selection.