Reliability and validity of the Infant and Toddler Quality of Life Questionnaire (ITQOL) in a general population and respiratory disease sample

OBJECTIVE: To evaluate feasibility, internal consistency, test-retest reliability, and concurrent and discriminative validity of the Infant and Toddler Quality of Life Questionnaire (ITQOL) for parents of pre-school children with 12 scales (103-items) covering physical and psychosocial domains and impact of child health on parents, in comparison with the TNO-AZL Pre-school Children Quality of Life Questionnaire (TAPQOL). METHODS: Parents of children from a random general population sample (2 months-4 years old; n = 500) and of an outpatient clinic sample of children with respiratory disease (5 months-[Formula: see text] years old; n = 217) were mailed ITQOL and TAPQOL questionnaires; a retest was sent after two weeks. RESULTS: Feasibility: The response was >or=80% with few missing and non-unique ITQOL-answers ( <2%) in both study populations. Some ITQOL-scales (3-4 scales) showed a ceiling effect (>25% at maximum score). Internal consistency: All Cronbach's alpha >0.70. Test-retest Intraclass Correlation Coefficients (ICCs) were moderate or adequate (>or=0.50; p < 0.01) for 10 ITQOL-scales. Validity: ITQOL-scales, with a few exceptions, correlated better with predefined parallel TAPQOL scales than with non-parallel scales. Five to eight ITQOL-scales discriminated clearly between children with few and with many parent-reported chronic conditions, between children with and without doctor-diagnosed respiratory disease and with a low and a high parent-reported medical consumption (p < 0.05). CONCLUSIONS: This study supported the evidence that the ITQOL is a feasible instrument with adequate psychometric properties. The study provided reference ITQOL scores for gender/age subgroups. We recommend repeated evaluations of the ITQOL in varied populations, especially among very young children, including repeated assessments of test-retest characteristics and evaluations of responsiveness to change. We recommend developing and evaluating a shortened ITQOL version