- •In this large sample of 1,567 interventions studied within Cochrane reviews, effects of most interventions (94%) interventions were not supported by high-quality evidence.
- •Potential harms of healthcare interventions were measured more rarely than benefits.
- •Patients, doctors, and policy makers should consider the lack of high-quality evidence supporting the benefits and harms of many interventions in their decision-making.
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Registration: PROSPERO: CRD42021240989.
Funding source: This study was not externally funded.
Declaration of interest: None of the authors have any personal financial interests or professional relationships to disclose.
Contributions: JH (guarantor) conceived of the idea (together with StS), and wrote the first draft of the protocol all authors contributed to developing the protocol. JH piloted the data extraction form and all authors made suggestions for improvement. JH, DK, TJ, CM, ML, HW, SeS, JS, NP, StS, and JPAI contributed to the data extraction. SeS developed a computerized quality check; HW and JH resolved discrepancies. JH, JPAI, CM, and DK developed a plan for and analyzed the data. JH drafted the final manuscript, with contributions from all authors.