“…Several approaches were used in the natural experiments as shown in Table 2 . From pre- and post-cohorts with a control group or prospective cohorts ( 36 , 38 , 43 , 52 , 53 , 60 ), controlled before and after studies ( 40 , 46 – 48 , 57 , 59 , 62 ) before and after studies with and without a control group ( 49 – 51 , 54 , 55 ), as well as quasi-experimental ( 37 , 56 ), cross-sectional pre- and post-intervention studies with or without a control group ( 35 , 39 , 41 , 42 , 58 , 61 ) providing repeated measures and retrospective studies ( 44 , 45 ). The 24 studies indicated that they were working on PA policies worldwide or nationally, but 25% did not specify the specific PA policy Using natural experiments to evaluate population health interventions: new Medical Research Council guidance ( 36 , 44 , 47 , 51 , 59 , 62 ), 37.5% described the PA policy, but did not evaluate its development ( 35 , 37 , 40 – 42 , 55 , 57 , 58 , 60 ) and the remaining studies were framed within national public policies on PA or active transportation clearly showing the evaluation of implementation at the level of parks, cities, schools or active transportation ( Table 2 ).…”