BACKGROUND: Systematic reviews cataloguing the barriers to and facilitators of various outcomes are increasingly popular, despite criticisms of this type of review on philosophical, methodological, and practical grounds. The aims of this review are to appraise, analyse, and discuss the reporting and synthesis practices used in recently published barriers and facilitators reviews in health services research.

METHODS: All English-language peer-reviewed systematic reviews that synthesised research on barriers and facilitators in a health services context were eligible for inclusion. We searched 11 databases over a thirteen-month period (November first 2017-November 30th 2018) using an exhaustive list of search terms for "barrier(s)", "facilitator(s)", and "systematic review".

RESULTS: One hundred reviews were included. We found a high degree of variation in the synthesis practices used in these reviews, with the majority employing aggregative (rather than interpretive) approaches. The findings echo common critiques of this review type, including concerns about the reduction of complex phenomena to simplified, discrete factors. Although several reviews highlighted the "complexity" of barriers and facilitators, this was usually not analysed systematically. Analysis of the subsample of reviews that explicitly discussed the barriers and facilitators approach revealed some common issues. These tended to be either conceptual/definitional (eg, ideas about interrelationships and overlap between factors) and methodological/practical (eg, challenges related to aggregating heterogeneous research).

CONCLUSION: Barriers and facilitators reviews should (1) clearly operationally define "barrier" and 'facilitator', (2) explicitly describe how factors are extracted and subsequently synthesised, and (3) provide critical reflection on the contextual variability and reliability of identified factors.