Recruitment and Consent in an observational study - Appendix: Appendix

Abstract Objective:The study sought to explore the consent rate and associated potential bias across a cohort in a large longitudinal population based study. Research design: Data were taken from a study designed to examine the effects of the reintroduction of community water fluoridation on children’s oral health over a five-year period. Children were recruited from a fluoridated and non-fluoridated area in Cumbria referred to as Group 1 and Group 2. Results: Data were available for 3138 individuals. The consent rate was shown to be significantly different between the two groups recruited from different locations. Consent was 12.91 percentage points lower in Group 2 compared to Group 1 (95% CI -16.27 to -9.56, p<0.001). The population in Group 2 were overall more deprived than Group 1 before consent was taken. Consent was not associated with deprivation in either group ( (4)=3.55, p=0.471 and (4)=7.81, p=0.099 for Group 1 and Group 2 respectively). Conclusion: The cohort within this study appeared to be unaffected by IMD-related non-consent. However there was a difference in consent rate between the two groups. With the population in Group 1 being significantly different from the population in Group 2 in relation to deprivation, it will be important to incorporate these differences into the analysis at the end of this longitudinal study.