Impact of SMS Messaging on Participation in Colorectal Cancer Screening

This study is a pragmatic, randomized, parallel-group clinical trial with a 1:1 allocation ratio, conducted within the framework of the Colorectal Cancer Early Detection Program (PDPCCR) in the Vallès Occidental region. The trial is coordinated by the Cancer Screening Unit of the Consorci Corporació Sanitària Parc Taulí. Operational Flow and Randomization: The study follows a sequential recruitment process. At Week 0, the entire target population receives a standard invitation letter according to the program's usual standard of care. For individuals who have not participated by Week 5, a computer-generated randomization sequence (Microsoft Excel) is applied weekly to assign them to either the intervention or control group. This weekly approach ensures the intervention is timely and integrated into the program's existing administrative workflow. Intervention Logistics: The Intervention Group receives a one-way SMS reminder sent via the 'Alhora' platform, the secure institutional messaging system used by the screening program. The content of the SMS was previously optimized and validated through a qualitative pilot study involving semi-structured interviews to ensure high readability and cultural acceptability among the target population. Non-participants in both groups receive the standard postal reminder letter at Week 6. Statistical Analysis Plan: The analysis will be conducted on both an intent-to-treat (ITT) and per-protocol basis. Descriptive statistics will report frequencies and medians with interquartile ranges (25th-75th percentiles). Bivariate analysis will utilize Chi-square tests for participation rates and the Mann-Whitney U test for response time differences. To estimate the effect size, Relative Risks (RR) with 95% confidence intervals will be calculated. Furthermore, a multivariate binary logistic regression will be performed using Jamovi software to adjust for potential confounders such as sex, age, geographic area, and history of previous participation