Research
Mixed
Natural experiments with weaker study designs (cross-sectional, case-only) are more likely to report positive associations with interventions than those with strong designs (longitudinal with comparison groups).
Be skeptical of positive findings from single-site, cross-sectional studies of policy changes. Prioritize longitudinal studies with comparison groups for evidence-based decision making.
StrongSupportsHIGH confidence
Studies varied widely in the strength of their design and studies with weaker designs were more likely to report associations in the positive direction.
Why this rating
Directly stated in the summary of the review.
Source
Impact of policy and built environment changes on obesity‐related outcomes: a systematic review of naturally occurring experiments
Stephanie L. Mayne et al. · Obesity Reviews · 2015
systematic_reviewCited 299×
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