The effects of reminders for colorectal cancer screening: participation and inequality.

PURPOSE: To investigate the effect of sending out reminders for colorectal cancer screening on socioeconomic and demographic inequalities in screening uptake. METHODS: All citizens aged 50-74 in Denmark are invited every 2 years for colorectal cancer screening. Non-participants receive an electronically distributed reminder. Data for these analyses were derived from national registers. Socioeconomic status was measured by income and educational level. Demographic variables included age, gender and marital status, and the analyses were stratified by immigration status. Logistic regression analyses were conducted to estimate the odds of non-participation for invited citizens and for reminded citizens divided by socioeconomic and demographic predictors. RESULTS: Of 763,511 native Danes invited for screening from 2014 to 2015, 387,116 (50.70%) participated after the initial invitation and 133,470 after receiving a reminder. Differences in participation were present in relation to all subgroups among both the invited citizens and reminded citizens. Differences persisted after full model adjustments with reductions for demographic variables. Odds ratio (OR) for non-participation in the eldest age group was 0.32 (95% CI, 0.32; 0.33) before and 1.11 (95% CI 1, 0.08; 1.14) after the reminder, compared to those under 55 years. OR for the 4th income quartile was 0.54 (95% CI, 0.53; 0.55) before and 0.44 (95% CI, 0.43; 0.45) after the reminder, compared to 1st quartile. CONCLUSIONS: Reminders increased the overall participation, and the inequalities in participation in relation to demographic factors were reduced after the distribution of reminders. The age differences were especially reduced. The inequalities in participation related to socioeconomic status were, however, slightly increased after reminder distribution.