A low proportion of systematic reviews in physical therapy are registered: a survey of 150 published systematic reviews.

BACKGROUND: Systematic reviews provide the best evidence about the effectiveness of healthcare interventions. Although systematic reviews are conducted with explicit and transparent methods, discrepancies might occur between the protocol and the publication.

OBJECTIVES: To estimate the proportion of systematic reviews of physical therapy interventions that are registered, the methodological quality of (un)registered systematic reviews and the prevalence of outcome reporting bias in registered systematic reviews.

METHODS: A random sample of 150 systematic reviews published in 2015 indexed on the PEDro database. We included systematic reviews written in English, Italian, Portuguese and Spanish. A checklist for assessing the methodological quality of systematic reviews tool was used. Relative risk was calculated to explore the association between meta-analysis results and the changes in the outcomes.

RESULTS: Twenty-nine (19%) systematic reviews were registered. Funding and publication in a journal with an impact factor higher than 5.0 were associated with registration. Registered systematic reviews demonstrated significantly higher methodological quality (median=8) than unregistered systematic reviews (median=5). Nine (31%) registered systematic reviews demonstrated discrepancies between protocol and publication with no evidence that such discrepancies were applied to favor the statistical significance of the intervention (RR=1.16; 95% CI: 0.63-2.12).

CONCLUSION: A low proportion of systematic reviews in the physical therapy field are registered. The registered systematic reviews showed high methodological quality without evidence of outcome reporting bias. Further strategies should be implemented to encourage registration.