Effects of a Co-Design–Based Invitation Strategy on Participation in a Preventive Health Check Program: Randomized Controlled Trial
Authors: Thilsing Trine , Larsen Lars Bruun , Sonderlund Anders Larrabee , Andreassen Signe Skaarup , Christensen Jeanette Reffstrup , Svensson Nanna Herning , Dahl Marie , Sondergaard Jens 
Published: February 2021

Background
Preventive primary care programs that aim to reduce morbidity and mortality from lifestyle-related diseases are often affected by low-to-moderate participation rates. Improving participation rates is essential for clinical effectiveness and cost-effectiveness. In 2016-2017, we conducted a pilot study (TOF pilot1) for a preventive primary care intervention (TOF is the Danish abbreviation for “Early Detection and Prevention”). Among 8814 invited patients, 3545 (40.22%) consented to participate, with the highest participation rates among women and patients with higher income, education, and employment.

Objective
The aim of this study was to evaluate the effects of a revised invitation strategy on invitation comprehensibility, the overall participation rate, and participant demography. The new strategy specifically targeted men and patients of low educational attainment.

Methods
This study was embedded in the second TOF pilot study (TOF pilot2, initiated in October 2018) that tested an adjusted intervention. The revised invitation strategy comprised a prenotification postcard and a new invitation that specifically targeted men and patients of low educational attainment. The new invitation was developed in a co-design process that included communication professionals and target-group representatives. The study sample consisted of 4633 patients aged between 29 and 59 years, who resided in one of two municipalities in the Region of Southern Denmark. Eligible patients were randomly assigned to one of four invitation groups. The control group (Group 1) received the original invitation used in TOF pilot1. The intervention groups received the original invitation and the prenotification postcard (Group 2), the new revised invitation and the prenotification postcard (Group 3), or the new invitation but no prenotification postcard (Group 4).

Results
Overall, 2171 (46.86%) patients consented to participate. Compared to the control group, participation rates increased significantly in all three intervention groups (all P<.001). Participation across the three intervention groups increased for women and men, as well as for patients with high and low educational attainment and high and low family income. The largest relative increase in participation rates occurred among men, patients with low educational attainment, and patients with low family income. No increase in participation was detected for unemployed patients or patients of non-Danish origin. Most participants found the original (813/987, 82.37%) and new (965/1133, 85.17%) invitations easy to understand with no significant difference (P=.08) in comprehensibility between invitations.

Conclusions
The results suggest that participation in preventive primary care interventions can be greatly increased by implementing a co-design–based invitation strategy that includes prenotification postcards and targeted invitations. Although firm conclusions cannot be made from this study, the observed increased participation rates for men and patients of low socioeconomic status may be relevant in programs that aim to reduce social inequality in health.

Trial Registration
ClinicalTrials.gov NCT03913585; https://clinicaltrials.gov/ct2/show/NCT03913585