Exploring how to evaluate a qualitative patient-centered outcome measure: literature review and illustrative example - a Perthes child-friendly measure.

To explore the question of 'how to evaluate a qualitative patient-centred outcome measure', comprising predominantly open-ended items, including perhaps emojis, story writing and/or pictures, in a way that does not compromise the strictures of the qualitative paradigm, doing so in a credible and authoritative manner. The paper aims to promote debate and discussion in the measurement validation community.Comprehensive literature review of three electronic databases (PubMed; SCOPUS; Web of Science/Knowledge) and searches of three outcome-focused journals.The vast majority (>90%) of the papers only used qualitative methods in the initial, in particular, content validation of a measure and then used (quantitative) psychometric validation procedures.  The remaining papers comprised articles that were either methodologically or methods focused and the role of qualitative research.  A number of key issues are raised, inter alia: giving primacy to the patient's perspective; exploring the meaning and interpretation respondents place on the concept and possible items in a measure; prioritising maximising meaningful discrimination from the respondent's perspective; ensuring face and content validity and relevance of items in the item content pool; and using appropriate qualitative methods, for example, concept elicitation, "think-aloud" and cognitive interviews and expert respondent panels/judges. This approach is applied to validate a child-friendly outcome measure for children with Perthes disease, a paediatric hip condition presenting primarily amongst male children aged 5-8 years.The core messages are to: (i) not force validation of a qualitative outcome measure into psychometric validation; but (ii) retain full adherence to the principles of the qualitative paradigm and employ procedures drawn from that paradigm. In this manner, primary emphasis would lie on issues of meaningfulness, face and content validity, the meaning of item and measure scores to respondents and, for a child-friendly measure, the child-friendliness of the measure.