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Table 4 Contributions of evidence from the major categories of research approaches

From: Hierarchies of evidence applied to lifestyle Medicine (HEALM): introduction of a strength-of-evidence approach based on a methodological systematic review

Research Method Unique contribution to understanding
Basic science Mechanisms of action
Intervention studies in humans / RCTs Reliable attribution; control of bias, confounding
Observational epidemiology; large and diverse population-based samples Effects at scale
Observational epidemiology; long time periods Duration of effects