Psychometric properties of the Pediatric Motor Activity Log used for children with cerebral palsy

The Pediatric Motor Activity Log (PMAL) is a parent-report measure of the use, by children with hemiplegic cerebral palsy (CP), of their affected upper limb in everyday activities. The aim of this study was to examine the psychometric properties of both scales of the PMAL ('How Often' and 'How Well' scales) using Rasch measurement modelling. Sixty-one parents of children with hemiplegic CP completed the PMAL and 31 completed it again 3 weeks later. The mean age of children was 4 years 6 months (SD 1y 9mo); 35 males, 26 females. Children were at Gross Motor Function Classification System (GMFCS) levels I (83%) and II (17%), and Manual Ability Classification System levels I (35%), II (52%), and III (14%). The original scales were found to have disordered rating scale structure. Further Rasch modelling with collapsed rating scale structures resulted in both scales conforming to the expectations of the Rasch model, yielding strong evidence for construct validity and reliability. One item from the How Often scale failed to conform to Rasch expectations and was deleted in subsequent analyses. Test-retest reliability of both scales was high (the intraclass correlation coefficient for the How Often scale was 0.94, and for the How Well scale 0.93). The revised scales possess good psychometric properties, specifically a logical item hierarchy, evidence of unidimensionality, adequate rating scale structure, and good test-retest reliability. We conclude that the revised PMAL has the capacity to yield valid and reliable scores except for children at the extremes of upper limb ability.