Interpreting population reach of a large, successful physical activity trial delivered through primary care
Failure to include socio-economically deprived or ethnic minority groups in physical activity (PA) trials may limit representativeness and could lead to implementation of interventions that then increase health inequalities. NICE guidelines called for more research to determine which interventions are effective and cost-effective in increasing activity levels among lower socio-economic and high risk groups. Randomised intervention trials often have low recruitment rates and rarely assess recruitment bias. A previous successful trial by the same team, PACE-Lift, using similar methods recruited 30% of the eligible population but was in an affluent setting with few non-white residents, was limited to those over 60 years of age.
PACE-UP is a large, effective, population-based walking trial in inactive 45-75 year-olds that recruited through seven London general practices using postal invitations send from the practice. Anonymised practice demographic data were available for all those invited, enabling investigation of inequalities in trial recruitment. Those not wishing to take part in the trial were invited to complete a questionnaire.We used practice data to calculate the participation rates for various subgroups and then calculated ratios for men v women, younger v older individuals and Black or Asian individuals compared with white individuals.We used questionnaire data to investigate co-morbidities and reasons for non participation.
From 10927 postal invitations, 1150 (10.5%) completed baseline assessment. Participation rate ratios (95% CI), adjusted for age and gender as appropriate, were lower in men 0.59 (0.52, 0.67) than women, in those under 55 compared with those ≥65, 0.60 (0.51, 0.71), in the most deprived quintile compared with the least deprived 0.52 (0.39, 0.70) and in Asian individuals compared with whites 0.62 (0.50, 0.76). Black individuals were equally likely to participate as white individuals. Participation was also associated with having a co-morbidity or some degree of health limitation. The most common reasons for non-participation were considering themselves as being too active or lack of time.
Conducting the trial in this diverse setting reduced overall response compared with our previous trial, with lower response in socio-economically deprived and Asian sub-groups. Trials with greater reach are likely to be more expensive in terms of recruitment and gains in generalizability need to be balanced with greater costs. Differential uptake of successful trial interventions may increase inequalities in PA levels and should be monitored.