Overview of systematic reviews - a new type of study. Part II

CONTEXT AND OBJECTIVE

Overviews of Systematic Reviews (OoRs) are a new type of study in which multiple evidence from systematic reviews (SRs) is compiled into an accessible and useful document. The aim here was to describe the state of the art and critically assess Cochrane OoRs that have been published.

DESIGN AND SETTING

Descriptive study conducted at a research center.

METHODS

The OoRs identified through the filter developed in Part I of this study were evaluated in five domains: methodological quality; quality of evidence; implications for practice; general profile of OoRs; and length of work.

RESULTS

All 13 OoRs included had high methodological quality. Some OoRs did not present sufficient data to judge the quality of evidence; using sensitivity analysis, the quality of evidence of the OoRs increased. Regarding implications for practice, 64% of the interventions were judged as beneficial or harmful, while 36% of them showed insufficient evidence for judgment. It is expected (with 95% confidence interval) that one OoR will include 9,462 to 64,469 patients, 9 to 29 systematic reviews and 80 to 344 primary studies, and assess 6 to 21 interventions; and that 50 to 92% of OoRs will produce meta-analysis. The OoRs generated 2 to 26 meta-analyses over a period of 18 to 31 months.

CONCLUSION

The OoRs presented high methodological quality; the quality of evidence tended to be moderate/high; most interventions were judged to be beneficial/harmful; the mean length of work was 24 months. The OoR profile adds power to decision-making.

Overview of systematic reviews - a new type of study: part I: why and for whom?

CONTEXT AND OBJECTIVE

Healthcare decision-making is complex and should involve healthcare professionals, patients and the best level of evidence. The speed of information production creates barriers against keeping up to date. In this light, methodologists have proposed a new type of study: overviews of systematic reviews (OoRs). The aim here was to introduce and demonstrate the role of OoRs in information synthesis for healthcare professionals, managers, researchers and patients.

DESIGN AND SETTING

Time-series study conducted at the Brazilian Cochrane Center, jointly with the Postgraduate Program on Internal Medicine and Therapeutics, Discipline of Emergency Medicine and Evidence-Based Medicine, Department of Medicine, Federal University of São Paulo.

METHODS

To show the growth in the numbers of published papers that provide high-level evidence and thus demonstrate the importance of OoRs for synthesis and integration of information, three filters for study designs were applied to two databases. An equation for predicting the expected number of published papers was developed and applied.

RESULTS

Over the present decade, the number of randomized controlled trials in Medline might reach 2,863,203 and the number of systematic reviews might reach 174,262. Nine OoRs and 15 OoRs protocols have been published in the Cochrane Library.

CONCLUSIONS

With the exponential growth of published papers, as shown in this study, a new type of study directed especially towards healthcare decision-makers was proposed, named "overview of systematic reviews". This could reduce the uncertainties in decision-making and generate a new hierarchy in the pyramid of evidence.