Structural validity of the Pain Interference Questionnaire and Fear of Pain Questionnaire for children and young people with cerebral palsy

Aim
To examine the structural validity and internal consistency of the Pain Interference Questionnaire for Cerebral Palsy (PIQ-CP) and Fear of Pain Questionnaire-Adapted for Cerebral Palsy (FOPQ-CP) measures and describe the proportion able to self-report, including individuals with diverse cognitive and communication abilities.

Method
This was a prospective cross-sectional study that included individuals with cerebral palsy (CP) aged 5 to 30 years, who completed the PIQ-CP and FOPQ-CP. Confirmatory factor analysis was used to assess structural validity and Cronbach's alpha (α) was used to assess internal consistency (self-report data only). Self-report and parent-report data were used to determine the proportion able to self-report.

Results
Self-report data showed good fit to the hypothesized model: one-factor PIQ-CP (n = 115; confirmatory fit index = 0.964, standardized root mean square residual = 0.078, α = 0.89) and two-factor FOPQ-CP (n = 102; confirmatory fit index = 0.937, standardized root mean square residual = 0.087, α = 0.68 [fear], α = 0.80 [avoidance]). Across all participants (n = 128), 79% could self-report, 11% required additional parent-report because self-report accuracy was uncertain, and 10% required parent-report only because of severe cognitive impairment.

Interpretation
The PIQ-CP and FOPQ-CP have sufficient structural validity and internal consistency and provide access to self-report in most children and young people with CP. They can now support equitable assessment of the impact of chronic pain in children and young people with CP, including those with diverse abilities.