<p>Patient reported outcome measures (PROMs) now play a significant role in randomized control trials (RCTs) providing the basis for efficacy or safety endpoints. Most PROM data is quantitative and is summarized at the group level. Whilst PROM data is informative in providing the aggregated patient perspective on disease and interventions, it provides little information about the patients’ individual experiences. For this, qualitative ‘case study’ research is needed. However, qualitative case-study research has traditionally not been considered as robust for establishing causal inference due to its singular nature and lack of quantifiable findings. The focus of this paper was to advance a proposal as to how to produce a single mixed-methods case analysis of an individual’s experiences with treatment from PROM and narrative data that can be used in causal inference research; so-called “Causal singularism”.</p>