Content validation of the COST for patient questionnaire (COPAQ) for patients with low back pain: a qualitative study

Introduction: The costs of low back pain (LBP) are complex and difficult to estimate. This study aims to adapt the Cost for Patients Questionnaire (CoPaQ) for use in LBP populations. Materials and methods: In a cross-sectional qualitative study, we conducted cognitive interviews to assess the CoPaQ's suitability for addressing costs related to LBP. Three groups of participants were included (n = 5 each): (i) persons with a history of LBP or primary caregiver, (ii) researchers with expertise in LBP, and (iii) primary care providers specialized in treating LBP. The interpretation, analysis, and summary of results used Knafl et al.'s qualitative content analysis method. Results: Persons with a history of LBP (n = 5), had a median age of 60 years (Interquartile Range (IQR): 26-71.5), and varying durations of LBP, the median duration of LBP 7 years (IQR: 4-32.5). Researchers (n = 5) had a median age of 33 years (IQR: 29-45). Primary care providers (n = 5) had a median age of 40 years (IQR: 37.5-65), and a background in chiropractic care (n = 3) and physiotherapy (n = 2). Content analysis of the interviews revealed sources of error with five pre-determined themes (clarity/comprehension, relevance, inadequate response definition, reference point, perspective modifiers) and one developed theme (organization). We modified the questionnaire for LBP populations based on the feedback. Conclusion: Our study evaluated the content validity of a questionnaire that assesses the direct and indirect costs associated with LBP. Future studies should pilot this questionnaire with persons of varying LBP severity and compare it with cost diaries.