Rasch Measurement Properties of the KIDSCREEN Quality of Life Instrument in Children with Cerebral Palsy and Differential Item Functioning between Children with and without Cerebral Palsy

ObjectiveTo assess if the Rasch-scaled KIDSCREEN-52 generic health-related quality of life measure was valid in children with cerebral palsy (CP).MethodsThe Rasch measurement properties and differential item functioning (DIF) of the KIDSCREEN-52 were examined in children with CP. Data were available from the KIDSCREEN project from 3219 children aged 8 to 12 years and 2126 parents in the general population; and from the SPARCLE project from 501 children aged 8 to 12 years with CP and 823 parents. Analysis used Zumbo's logistic regression DIF approach. Partial credit model analyses were conducted.ResultsAll items of the KIDSCREEN self-report version fitted the partial credit model (smallest P-value: 0.256). Only one item of the parent version did not fit the data well (smallest P-value 0.001). Statistically significant DIF was observed in some items, but was of substantial magnitude (ΔR2 = 0.046, 0.049) for only two items in two dimensions of the parent version. The practical impact of DIF was small. DIF-adjusted standardized mean differences between children with and without CP being 1.07 and 0.34 for the physical and school dimensions, respectively (unadjusted: 1.09 and 0.16).ConclusionThe KIDSCREEN-52 functions in a similar way in children with CP and in the general population. Comparisons of quality of life between such children are therefore likely to be valid.