Psychometric properties of the Spanish version of the Activities Scale for Kids (ASK): reliability, validity and the Rasch model

Aims: To evaluate the psychometric properties of the Spanish version of the Activities Scale for Kids capability (ASKc) and ASK performance (ASKp) questionnaires.

Design: It includes an analysis of different types of reliability (internal consistency, test-retest, inter-rater, Rasch model) and validity (convergent and discriminant) values.

Settings: The sample was recruited in schools, associations and one hospital in Spain.

Participants: The main sample comprised 448 children (114 with disabilities); and 96 parents of the group of 114 children with disabilities, along with 2 therapists.

Methods and procedure: Children with physical disabilities completed questionnaires at two different time points; while healthy children only once. Both ASK questionnaires were also administered to parents. Therapists observed 69 children in 15 of the 30 activities listed in the ASKc.

Primary and secondary outcome measures: ASKc and ASKp were used to measure physical disability among children. The Childhood Health Assessment Questionnaire (CHAQ), The Screening For and Promotion of Health-Related Quality of Life in Childrenand Adolescents - a European Public Health perspective (KIDSCREEN), Gross Motor Function Classification System (GMFCS), Manual Ability Classification System (MACS) and Functional Mobility Scale (FMS) were used to analyse convergent validity.

Results: Excellent values were obtained for the reliability of the scale. Internal consistency was >0.95 (Cronbach's α) for both questionnaires. The intraclass correlation coefficient test-retest reliability was 0.94 (ASKc) and 0.93 (ASKp). Correlations between parents' and children's scores were 0.91(ASKc) and 0.90 (ASKp); and the correlation between therapists' and children's scores was 0.78. The Rasch analysis indicated that the Spanish version had a unidimensional structure. Furthermore, the results revealed adequate validity indices. Both ASK questionnaires correlated significantly with the CHAQ, three dimensions of the KIDSCREEN and the GMFCS, MACS and FMS. Finally, children without disabilities had higher ASKc and ASKp scores than children with disabilities (p=0.0001).

Conclusions: Both the ASKc and the ASKp versions are reliable and valid instruments that can be used to measure the capabilities of Spanish-speaking children, whose responses also demonstrate their own reliability as informants of the impact of disability on the activities of daily living.