Health-related quality of life (HRQOL), a multidimensional construct that assesses several domains (e.g., physical, emotional, social), is an important patient-reported outcome (PRO) in obesity research. PROs are used as primary and secondary endpoints for clinical trials if basic psychometric standards (i.e., good reliability and validity) are met and information is provided to evaluate the smallest clinically relevant change a patient perceives, known as the minimal clinically important difference (MCID)(1
The sensitivity and specificity of weight/obesity-specific measures make them well-suited as PROs for clinical trials. Several such measures exist(2
), including a self-report for adolescents, the Impact of Weight on Quality of Life-Kids(4
). Initial psychometric evaluation of the IWQOL-Kids, has demonstrated excellent scale reliabilities, convergent and discriminant validity, and responsiveness(4
). However, test-retest reliability and the establishment of MCIDs have not been conducted.
MCIDs can be established using anchor-based or distribution-based methodologies. Anchor-based methods utilize changes on clinically-relevant rating scales (e.g., within-patient global ratings of change) to serve as anchors when establishing the MCID. Although easy to obtain and based on the patient’s perspective, these methods are limited by measurement imprecision, unknown reliability, and a lack of reliability of the specific global rating of change scales(5
). Distribution-based methods rely on statistical procedures to determine the MCID, including the one standard error of measurement (SEM) method, (5
) which has been used to establish MCIDs for a popular pediatric generic HRQOL measure, the PedsQL(7
). This approach is sample-independent, accounts for measurement precision, and is expressed in the units of the measure. Furthermore, studies have demonstrated that one SEM consistently mapped on to MCIDs established with anchor-based methods(8
). The aims of the current study were to evaluate test-retest reliability and establish distribution-based MCIDs for the IWQOL-Kids scales.