Table 4 Way forward and research agenda for CERQual

The following steps are needed to further develop the approach:

 • To date, there is little collective experience of applying CERQual in the context of mixed method syntheses that include qualitative and quantitative data. Whether the approach needs to be adapted for this context needs to be explored. An important concern is whether assessing the quantitative and qualitative elements of a mixed-methods study individually, using separate approaches, risks under-valuing the contribution of review findings based on integrated data

 • In some decision making processes, CERQual assessments of qualitative evidence may be presented alongside other GRADE assessments for data on intervention effectiveness and resource use.User testing is needed to explore how best to present this range of assessments to evidence users

 • Our aim is that CERQual can be applied to review findings based on any kind of qualitative data. However, we do not have experience of applying the approach to syntheses where the primary material includes sources that are textual in nature but are not the output of formal qualitative research procedures. Such sources include blogs, online discussion group transcripts or newspaper reports. Further work is needed to examine how the approach can be used for such data

 • We need to gather experience and, if necessary, adapt CERQual for syntheses of primary studies outside the field of health and health care research

 • We need further work on whether CERQual needs to be adapted for application to more interpretive outputs from syntheses, such as logic models and findings from synthesis methods such as meta-ethnography