Conducting a large, longitudinal, multi-site qualitative study within a mixed methods evaluation of a UK national health policy: reflections from the GPED study

Over the past decade, there has been a growing trend towards the use of ‘big qualitative data’ in applied health research, particularly when used as part of mixed methods evaluations of health policy in England. These ‘big qualitative’ studies tend to be longitudinal, complex (multi-site and multi-stakeholder) and involve the use of multiple methods (interviews, observations, documents) and large numbers of participants (n=100+). Despite their growing popularity, there is no methodological guidance or methodological reflection on how to undertake such studies. Qualitative researchers are therefore faced with a series of unknowns when designing large qualitative studies, particularly in terms of knowing whether existing qualitative sampling and analysis methods are appropriate in this context. In this paper, we use our experience of undertaking a big qualitative study, as part of a national mixed methods evaluation of a health policy in England to reflect on some of the key challenges that we faced in our qualitative study, which broadly related to: sample size, data analysis and the role of patient and public engagement. Underpinning these difficulties was the challenge of being flexible and innovative within the largely positivist research climate of applied health research and being comfortable with uncertainty relating to the three issues outlined. The reflections we present are not to be viewed as a method ‘how to’ guide, but rather as a platform to raise key issues relating to the qualitative methods that we found challenging, in order to stimulate discussion and debate amongst the qualitative community. Through this paper, we therefore hope to demystify what it is like to undertake such a study and hope to spark much needed discussion and innovation to support the future design and conduct of qualitative research at scale.