The Portuguese DISABKIDS Asthma Module: a global index of asthma-specific quality of life for children and adolescents

Background: The KIDSCREEN and DISABKIDS questionnaires constitute a modular system for assessing the health-related quality of life (HrQoL) of children/adolescents. Objective: This study was aimed at examining the factorial structure of the Portuguese patient-and parent-reported versions of the DISABKIDS-Asthma Module (AsM) and its invariance across age groups and informants, as well as to examine their reliability and construct validity. Methods: The sample included 140 children/adolescents aged 8-18 years, who were diagnosed with asthma, and one of their parents. Both family members assessed HrQoL at the generic (KIDSCREEN-10), chronic-generic (DISABKIDS-12) and asthma-specific (DISABKIDS-AsM) levels. Asthma severity was classified by physicians using Global Initiative for Asthma (GINA) guidelines. Results: Confirmatory factor analysis attested the factorial validity of the correlated two-factor model of the DISABKIDS-AsM, but the low average variance extracted by each factor (Impact and Worry) suggested that a one-factor structure would better fit the Portuguese data. The one-factor model had an acceptable fit (chi(2)/df 1.97; comparative fit index=0.94; root mean square error of approximation =0.08) and was invariant between age groups (children vs. adolescents) and informants (patient-reports vs. parent-reports). The resulting global index of asthma-specific HrQoL presented good reliability and convergent validity with the generic and chronic-generic measures. The DISABKIDS instruments also detected significant differences in HrQoL regarding asthma severity groups. Conclusions: The DISABKIDS-AsM may be regarded as a specific one-dimensional questionnaire, which, besides suiting pediatric patients in different developmental stages and enabling reliable proxy-reports, is sensitive to asthma clinical characteristics and is cross-culturally comparable, thus representing a valuable tool for assessing asthma-specific HrQoL as a primary health outcome in clinical practice and research contexts.