Understanding changes in soft drinks marketing after introduction of the UK Soft Drinks Industry Levy: developing a theory of change by use of concept mapping and stakeholder interviews

Abstract Background In 2018, the UK government introduced a Soft Drinks Industry Levy (SDIL) to reduce the consumption of sugary drinks and their health consequences. Taxes on sugary drinks might prompt changes in associated marketing, but whether and how this happens, and the implications for health, are unclear. To inform exploration of changes in sugary drinks marketing that might result from the SDIL, we developed a theory of change by use of concept mapping and stakeholder interviews. Methods We used concept mapping, an inductive technique, to develop an initial theory. We then elaborated this theory on the basis of one-to-one telephone interviews with six representatives of each of industry, academia, and civil society (total n=18), who had experience of strategic decision-making or marketing by sugary drinks firms. Interviewees were recruited using seed and snowballing sampling. Interviews explored motivations for and manifestations of changes in soft drink marketing. Interviews were transcribed verbatim and thematically analysed. To maximise trustworthiness, four transcripts were double-coded, the revised theory was informally peer reviewed, three transcripts were excluded from initial coding to allow comparison with the revised theory, and the resultant theory was validated by interviewees. Findings The initial theory described strategic planning and decision-making followed by the analysis and selection of specific marketing responses. After analysis of interviews we developed this concept into an iterative and circular theory of marketing change. Briefly, firms change marketing by reviewing their internal and external context, identifying a catalyst, deciding their brand positioning, and then selecting a combination of strategies to enact this positioning. Resultant changes in purchasing feed back into factors internal and external to the firm. Ethics approval was granted by the University of Cambridge Humanities and Social Sciences Research Ethics Committee. Interpretation These findings extend understanding of industry responses to sugary drinks taxes and might be relevant for understanding of industry responses to fiscal interventions more generally. Our theory highlights that soft drinks firms are continually evolving, consider many external factors in addition to the SDIL, and think about marketing more broadly than just advertising. Our research was based on one case study of the SDIL; interviews were done 1 year after implementation of the levy. Future work should prospectively test our theory in alternative contexts. Funding JA and MW are funded by the Centre for Diet and Activity Research, a UK Clinical Research Collaboration Public Health Research Centre of Excellence. Funding from the British Heart Foundation, Cancer Research UK, Economic and Social Research Council, Medical Research Council, the National Institute for Health Research, and the Wellcome Trust, under the auspices of the UK Clinical Research Collaboration, is gratefully acknowledged. TP, JA and MW are funded by a grant from NIHR (16/130/01) to evaluate the UK Soft Drinks Industry Levy. HF receives funding for her PhD studentship from Public Health England and the Economic and Social Research Council. LL and FG are employed by Public Health England. MW holds an honorary consultant in public health contract with PHE. These funding sources had no direct role in the writing of the manuscript or decision to submit for publication.