Aims: A non-response rate of 20-40%is typical in questionnaire studies. The authors evaluate non-response bias and its impact on analyses of social class inequalities in health.
Methods: Set in the context of a health survey carried out among the employees of the City of Helsinki (non-response 33%) in 2000-02. Survey response and non-response records were linked with a personnel register to provide information on occupational social class and long sickness absence spells as an indicator of health status.
Results: Women and employees in higher occupational social classes were more likely to respond. Non-respondents had about 20-30% higher sickness absence rates. Relative social class differences in sickness absence in the total population were similar to those among either respondents or non-respondents.
Conclusions: In working populations survey non-response does not seriously bias analyses of social class inequalities in sickness absence and possibly health inequalities more generally.