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

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Abstract
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). 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–5 1/2 years old; n = 217) were mailed ITQOL and TAPQOL questionnaires; a retest was sent after two weeks. Feasibility: The response was ≥80% with few missing and non-unique ITQOL-answers (25% at maximum score). Internal consistency: All Cronbach’s α >0.70. Test–retest Intraclass Correlation Coefficients (ICCs) were moderate or adequate (≥0.50; p lt; 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). 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.