Exploring the content validity of the Chalder Fatigue Scale using cognitive interviewing in an ME/CFS population

Abstract

ABSTRACT Background The Chalder Fatigue Scale, also known as the Chalder Fatigue Questionnaire (CFQ) is a Patient Reported Outcome Measure (PROM) comprising 11 items designed to measure physical and cognitive fatigue. It is widely used with people with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). There is no published evaluation of the content validity of the CFQ. Objectives To elicit information regarding the cognitive processes undertaken by people living with ME/CFS, when completing the CFQ to allow examination of the CFQ’s content validity. Methods A qualitative study utilising semi-structured cognitive interviewing. All data were collated according to the CFQ item but some general criticisms of the content validity of the CFQ were also identified. Results The CFQ currently consists of one item clearly related to physical symptoms (1.6), four items clearly related to cognitive function (1.8, 1.9, 1.10, 1.11) and one item relating to fatigue (1.5) which could be interpreted as cognitive and/or physical fatigue. The other five items have been identified by participants as lacking clarity (1.1, 1.7), relating to behaviour not symptoms (1.2, 1.4), or relating to sleepiness not fatigue (1.3). Conclusion Participants provided a wealth of insight into the challenges related to relevance, comprehensiveness, and comprehensibility of the CFQ, indicating that revision is required. This strengthens the case for participation of people with lived experience at all stages of PROM development. There is a need for an assessment tool/PROM for clinical and research use ME/CFS which has undergone content validation involving people living with ME/CFS.