Impact of SMS Messaging on Participation in Colorectal Cancer Screening

This study is a pragmatic, randomized, parallel‐group clinical trial with a 1:1allocation ratio, conducted within the framework of the Colorectal Cancer Early DetectionProgram (PDPCCR) in the Vallès Occidental region. The trial is coordinated by the CancerScreening 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 accordingto the program's usual standard of care. For individuals who have not participated byWeek 5, a computer‐generated randomization sequence (Microsoft Excel) is applied weeklyto assign them to either the intervention or control group. This weekly approach ensuresthe intervention is timely and integrated into the program's existing administrativeworkflow.Intervention Logistics: The Intervention Group receives a one‐way SMS reminder sent viathe 'Alhora' platform, the secure institutional messaging system used by the screeningprogram. The content of the SMS was previously optimized and validated through aqualitative pilot study involving semi‐structured interviews to ensure high readabilityand cultural acceptability among the target population. Non‐participants in both groupsreceive 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 medianswith interquartile ranges (25th‐75th percentiles). Bivariate analysis will utilizeChi‐square tests for participation rates and the Mann‐Whitney U test for response timedifferences. To estimate the effect size, Relative Risks (RR) with 95% confidenceintervals will be calculated. Furthermore, a multivariate binary logistic regression willbe performed using Jamovi software to adjust for potential confounders such as sex, age,geographic area, and history of previous participation