Figure 2From: Effect of reminders on mitigating participation bias in a case-control study ORs and 95% CIs for Campylobacter risk factors in final multivariable model, by mailing round. Crosses: model using controls returning a questionnaire before being sent a reminder; Closed circles: model using controls returning a questionnaire before being sent a second reminder; Open squares: model using all controls. All models are additionally adjusted for sex, age group, study site and month.Back to article page