Precision and content range of a parent-reported item bank assessing lower extremity and mobility skills in children with cerebral palsy

Aim: The aim of this study was to determine the psychometric properties, content range, and measurement precision of a lower extremity physical functioning and mobility skills item bank (LE85) in children with cerebral palsy (CP). Method: Lower extremity functioning and mobility skill items were administered to 308 parents of children (169 males, 139 females; mean age 10y 8mo, SD 4y) with spastic CP (145 diplegia, 73 hemiplegia, 89 quadriplegia; [for one person type of CP was unknown]) classified using the Gross Motor Function Classification System (75 level I, 91 level II, 79 level III, 37 level IV, 26 level V). Additional legacy measures were administered to assess concurrent validity. Psychometric characteristics, differential item functioning, content range, and score precision were examined. Results: The LE85 had acceptable psychometric properties. Content range matched the ability range of the sample population and exceeded legacy measures with minimal differential item functioning. The LE85 had good correlation with the Paediatric Outcomes Data Collection Instrument, Functional Independence Measure for Children, Gillette Functional Assessment Questionnaire, and Paediatric Quality of Life Inventory - CP module (range r=0.63-0.86). Precision of the LE85 and 10-item simulated computer adaptive test scores outperformed legacy measures. Interpretation: The LE85 appears to be suitable to administer as a computer adaptive test to measure lower extremity physical functioning and mobility in children with CP.