Members of the ALSPAC cohort (mothers, fathers and their offspring) have been followed up for almost 25 years through regular questionnaires and clinics. ALSPAC does not have complete data for all original cohort members because some cohort members did not complete all the questionnaires or attend all the clinics. It has been shown that participants with missing data are different to participants without missing data in terms of social and lifestyle characteristics. However, we do not know which of these characteristics specifically influence whether a cohort member continues to participate in ALSPAC, because these characteristics tend to cluster together. In this research we will use genetic variants that are associated with lifestyle factors, for example, education, body mass index and smoking, to assess whether each of these factors cause non-response in the ALSPAC study. We will also try to identify additional genetic variants that are associated with missing data within ALSPAC. Understanding factors which influence whether an individual answers a questionnaire or attends a study clinic may help to improve response in ALSPAC and in other cohort studies.