How should we evaluate research on counselling and the treatment of depression? A case study on how the National Institute for Health and Care Excellence's draft 2018 guideline for depression considered what counts as best evidence.

Background: Health guidelines are developed to improve patient care by ensuring the most recent and 'best available evidence' is used to guide treatment recommendations. The National Institute for Health and Care Excellence's (NICE's ) guideline development methodology acknowledges that evidence needed to answer one question (treatment efficacy) may be different from evidence needed to answer another (cost-effectiveness, treatment acceptability to patients). This review uses counselling in the treatment of depression as a case study, and interrogates the constructs of 'best' evidence and 'best' guideline methodologies. Method: The review comprises six sections: (i) implications of diverse definitions of counselling in research; (ii) research findings from meta-analyses and randomised controlled trials (RCTs); (iii) limitations to trials-based evidence; (iv) findings from large routine outcome datasets; (v) the inclusion of qualitative research that emphasises service-user voices; and (vi) conclusions and recommendations. Results: Research from meta-analyses and RCTs contained in the draft 2018 NICE Guideline is limited but positive in relation to the effectiveness of counselling in the treatment for depression. The weight of evidence suggests little, if any, advantage to cognitive behaviour therapy (CBT) over counselling once risk of bias and researcher allegiance are taken into account. A growing body of evidence from large NHS data sets also evidences that, for depression, counselling is as effective as CBT and cost-effective when delivered in NHS settings. Conclusion: Specifications in NICE's updated guideline procedures allow for data other than RCTs and meta-analyses to be included. Accordingly, there is a need to include large standardised collected data sets from routine practice as well as the voice of patients via high-quality qualitative research.