“…In 7 studies, authors reported that some houses in the control group had received the intervention. [34][35][36]41,42,51,58 In around half of studies that reported housing conditions at baseline (7 of 15), most of the intervention households reported having no housing problems at baseline. 27,38,40,44,46,50,67 Contamination of the control group and the wide within-study variation in the housing improvements delivered (i.e., in the intervention integrity) probably limited the ability to detect impacts, and this may have led to an underestimate of the efficacy of housing improvement on health.…”