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BMC Public Health. 2018 Jan 23;18(1):170. doi: 10.1186/s12889-018-5034-4.

Interpreting population reach of a large, successful physical activity trial delivered through primary care.

Author information

Pragmatic Clinical Trials Unit, Queen Mary's University of London, London, SE 1 2AT, UK.
Department of Medical Statistics, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK.
Population Health Research Institute, St George's University of London, London, SW17 ORE, UK.
Gerontology and Health Services Research Unit, Brunel University, London, UB8 3PH, UK.
Research Department of Primary Care & Population Health, University College, London, NW3 2PF, UK.
Department of Sport Medicine, Norwegian School of Sport Sciences, PO Box 4014, 0806, Oslo, Norway.
MRC Epidemiology Unit, University of Cambridge, Cambridge, CB2 OQQ, UK.
Department of Public Health Sciences, Kings College London, London, SE1 1UL, UK.



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. Randomised intervention trials often have low recruitment rates and rarely assess recruitment bias. A previous trial by the same team using similar methods recruited 30% of the eligible population but was in an affluent setting with few non-white residents and 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. Anonymised practice demographic data were available for all those invited, enabling investigation of inequalities in trial recruitment. Non-participants were invited to complete a questionnaire.


From 10,927 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, 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.

TRIAL REGISTRATION: ISRCTN98538934 . Registered 2nd March 2012.


Non-participation; Physical activity; Primary care; Randomised trials; Recruitment

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