Umbrella reviews: A new tool to synthesize scientific evidence in surgery.

Researchers and practitioners are faced with an exponential increase in the number of systematic reviews (SRs) (with or without meta-analysis), a so-called `secondary' research method that synthesizes data from primary research. This growing number, sometimes with discordant results on the same subject or with non-conclusions, has led to the introduction of the concept of reviews to synthesize SR in order to combine scientific knowledge useful to practitioners. These so-called ``umbrella reviews'' (UR) constitute a new tertiary research tool. Surgical research is no exception to this development but umbrella surgical reviews remain relatively rare. Any UR must be transparent and meet rigorous methodological criteria. The UR could thus provide answers to practical questions in the field of surgery, but only on condition that the bias of the included SRs is limited. Let us not forget that the base requirement of clinical surgical research remains the good methodological quality of clinical studies (primary research). Only thus can SRs or URs (secondary or tertiary research) be more useful and decisive.