Adolescent body weight and health-related quality of life rated by adolescents and parents: the issue of measurement bias

BACKGROUND Evidence is sparse about whether body weight categories in adolescents are associated with differences in pediatric HRQoL rated by adolescents and parents. Additionally, it is unknown whether HRQoL rated by individuals with different body mass index (BMI) weight categories is psychometrically comparable. This study aimed to assess whether difference in pediatric HRQoL rated by adolescents and their parents was explained by BMI weight status, and to test measurement properties of HRQoL items related to weight categories using differential item functioning (DIF) methodology. DIF refers to the situation when the individuals across subgroups rate an item differently (e.g., item score three by one subgroup and four by another) given the same underlying construct. METHODS A cross-sectional study utilizing a sample of parents (n = 323) and their adolescents aged 15-18 years old (n = 323) who enrolled in Florida's Medicaid. Adolescent self-reports and parent proxy-reports of the Pediatric Quality of Life Inventory was adopted to measure pediatric HRQoL. We classified body weight categories as normal weight, overweight, and obesity. A Multiple Indicator Multiple Cause (MIMIC) method was used to assess DIF associated with BMI weight status, especially testing the disparity in the parameters of different weight categories (reference: lower weight category) associated with a response to a HRQoL item conditioning on the same underlying HRQoL. DIF analyses were conducted by adolescent self-reports and parent proxy-reports. RESULTS Parents reported lower pediatric HRQoL across all domains than adolescents did. Excess body weight (combined overweight and obese) was significantly associated with a greater discrepancy in the rating of emotional and total functioning between adolescents and parents (p < 0.05). DIF associated with BMI weight categories was identified by two items in adolescent self-reports and five items in parent proxy-reports. CONCLUSIONS Adolescents' BMI weight categories significantly contribute to a difference in the rating of pediatric HRQoL by adolescents and parents.