Objectives: Colloquial evidence (CE) has been described as the informal evidence that helps provide context to other forms of evidence in guidance development. Despite challenges around quality, and the potential biases, the use of CE is becoming increasingly important in assessments where scientific literature is sparse and to also capture the experience of all stakeholders in discussions, including that of experts and patients. We aimed to ascertain how CE was being used at the National Institute for Health and Care Excellence (NICE).

Methods: Relevant data corresponding to the use of CE was extracted from all NICE technical and process manuals by two reviewers and quality assured and analyzed by a third reviewer. This was considered in light of the results of a focused literature review and a combined checklist for quality assessment was developed.

Results: At NICE, CE is utilised across all guidance producing programmes and at all stages of development. CE could range from information from experts and patient/carers, grey literature (including evidence from websites and policy reports) and testimony from stakeholders through consultation. Six tools for critical appraisal of CE were available from the literature and a combined best practice checklist has been proposed.

Conclusions: As decisions often need to be made in areas where there is a lack of published scientific evidence, CE is employed. Therefore to ensure its appropriateness the development of a validated CE data quality check-list to assist decision makers is essential and further research in this area is a priority.