Article: The Devon Active Villages Evaluation (DAVE) trial of a community-level physical activity intervention in rural south-west England: a stepped wedge cluster randomised controlled trial. Solomon et al. International Journal of Behavioral Nutrition and Physical Activity 2014, 11:94.
Unit of clustering: village
Hypothesized effects: increased levels of physical activity after exposure to the intervention
Exposure measurement level: the exposure was “offering people of all ages increased opportunities to experience the enjoyment of sport and physical activity.” The precise nature of the intervention varied by village, but each village had at least three options that were targeted to different age groups so that the full range of ages was covered in each village. The intervention/exposure was measured at the group/cluster level (village) – e.g. when the village was randomized to receive the intervention.
Statistical model used to estimate the effect: the researchers used multilevel, random effects linear regression models for continuous outcomes, specifying the village effect as random; and marginal logistic regression models using generalized estimating equations (GEEs) for binary outcomes. Unadjusted and adjusted (for region, gender, and age) analyses were conducted.
Other statistical models: The authors could have considered using either mixed effects models or GEE models for all outcomes rather than using mixed for continuous and GEEs for binary. Considering the authors’ interest in determining the effects for all adults, a marginal approach like GEEs might have been preferable between the two.