Does Low Willingness to Respond Introduce a Bias? Results from a Socio‐epidemiological study among Young Men and Women

The aim of this study was to investigate if willingness to respond can introduce bias in a population survey and to study the socio‐economic characteristics of those with high and low willingness to respond. Two groups of final‐year pupils at compulsory school were surveyed five years after leaving school, at the age of 21. The data were collected during class meetings, by mailed questionnaires, telephone and personal interviews. The response rates in the studies were proportionally high – about 98% and 90% respectively. In both surveys there were more men compared to women who were late respondents or non‐respondents. Long‐term unemployment and lack of upper secondary school for both men and women, as well as living with a partner for men, corresponded to low willingness to respond to a survey. A higher alcohol consumption – between 1.5 to 6.5 times – was observed among those with lower willingness to respond. Even a low rate of non‐response can introduce a serious bias and produce uncertain results in, for example, studies on the consequences of youth unemployment on alcohol consumption.