Nudging Hard-to-Reach Populations Toward Spanish Colorectal Cancer Screening (JA PreventNCD study)

Introduction

Men over 60 are the least likely to participate in the Colorectal Cancer Screening Programme of the Valencia Community (CRCSP-VC). This study assesses three invitation-based behavioural nudges of increasing intensity to boost screening participation among never-screened men over 60 (hard-to-reach population).

Methods

A randomized controlled trial within the CRCSP-VC (Spain, Feb–Sep 2025) targeting never-screened men over 60 from the screening-eligible population, randomly assigned to one control and three intervention groups. The control group (n = 1,600) received the usual invitation (letter plus pre-paid card to accept the invitation; if accepted, the screening test was mailed home); Intervention groups (I) received escalating nudges: I1 (n = 1,600), usual invitation plus a modified letter using behavioural change messages; I2 (n = 1,600), I1 plus choice of pre-paid card or SMS to accept; I3 (n = 1,200), I1 plus direct home delivery of the screening test. Descriptive and multivariate (logit CI95%) analysis of the outcome variable (participation in CRCSP-VC), by region, age and socio-economic status (SES) (Q1=best to Q4=worst). Randomised Control Trial Registry: https://doi.org/10.1186/ISRCTN52248153. Ethics Committee approval (20241220/03/E).

Results

Participation rates were 5.4% (control group), 6.5% (I1), 7.7% (I2), and 19.7% (I3). Compared to controls, adjusted ORs were: I1 (OR1.20; CI 0.73-1.97); I2 (OR1.53; CI 0.94-2.50); and I3 (OR 4.30; CI 2.67-6.95). Participation increases in I3 vs control group in all SES levels (p < 0.05): (Q1: 4.2% vs 19.1%; Q2: 6.3% vs 22.0%; Q3: 1.7%-16.1%; Q4: 8.9% vs 20.8%).

Conclusions

Nudge intensity strongly predicts screening uptake. Directly mailing the screening test to participantśhome produced a four-fold participation increase, with consistent gains across all socioeconomic groups, suggesting this strategy can meaningfully reduce screening inequalities in hard-to-reach populations.

Key messages

• Participation rates increase significantly when the screening test is included directly with the invitation letter.

• Sending the screening test directly with the invitation letter reduces screening inequalities in hard-to-reach populations.