Association between variables used in the field substitution and post-stratification adjustment in the Belgian health interview survey and non-response

Field substitution and post-stratification adjustment have been proposed to reduce non-response bias in population surveys. We investigated if variables involved in those techniques in the Belgian health interview survey 2004 are associated with non-response and assessed the impact of field substitution and post-stratification adjustment on the survey results. Data were obtained from all selected households (n= 12.204). The association between non-response and the selected variables was explored through multilevel logistic regression models with municipality and statistical sector as random effects. All investigated variables were significantly related with non-response. Especially households that could not be contacted differed substantially from those who participated. Only post-stratification had a clear impact on the survey results. Even if variables used in the field substitution procedure of health surveys are strongly associated with non-response, the impact of field substitution on the survey results may be minimal, either because there was no bias of relevance or it was not captured. The usefulness of field substitution to correct for non-response bias in population health surveys seems to be quite limited.