Participants and Procedure
A total of 803 Dutch children under treatment for overweight, obesity or severe obesity, aged between 4 and 19 years, participated in this study. Data collection was part of multiple studies: 1) baseline data of a large cohort study [21] (HELIOS, N =120), in which children with severe obesity (ages 8–19) participated in an intensive inpatient treatment; 2) baseline data of an outpatient combined lifestyle intervention for children with all grades of overweight and obesity (ages 7–13) [26] (LEFF, N = 358); and 3) additional data collection via a newly developed webtool (N = 325) in the regular youth healthcare setting for children with overweight, obesity and severe obesity (ages 4–18). Baseline data were collected from 27 healthcare settings throughout the Netherlands before starting treatment, between 2016 and July 2018.
All generic and weight-specific HRQOL measures were prospectively collected and used for clinical as well as research purposes. Ethical approval was given by the medical ethics committee of VU University Medical Center Amsterdam for the first two studies, HELIOS and LEFF. For the additional data collection full ethical approval was waived by the same medical ethics committee, as data were collected for clinical care purposes. In all cases, data was only included when participants’ parents (and children over age 12) gave informed consent to use their scores for scientific purposes.
Measures
Generic health-related quality of life. The Pediatric Quality of Life Inventory (PedsQL) 4.0 [27] is a validated measure to assess generic HRQOL. In this study two versions were used: a child version for ages 8–12 and a teenager version for ages 13–18. The questionnaire consists of 23 items that can be divided into four scales: physical functioning, emotional functioning, social functioning and school functioning. The items were scored on a 5-point scale: 0 = never a problem, 1 = almost never a problem, 2 = sometimes a problem, 3 = often a problem, 4 = almost always a problem. Similarly to the original study [27], items were reverse-scored and linearly transformed to a 0–100 scale (0=100, 1=75, 2=50, 3=25, 4=0). A higher score represents a better generic HRQOL. The original PedsQL has a high reliability (Cronbach α on total score = 0.88, Cronbach α subscales range 0.68–0.90) and validity [28]. The reliability in this sample was good for the total scores (α = 0.99) and fairly good for the subscales (range α: 0.68–0.76).
Weight-specific Quality Of Life. The Impact of Weight on Quality of Life for Kids (IWQOL-Kids) [11] is a validated measure to assess weight-specific HRQOL. Two versions were used: a child version and a parent proxy version (Dutch translation [6, 23]). The IWQOL-Kids was developed and validated for the 11–19 age group. This range was pragmatically chosen by the developers [11]. Although reliability and validity is not known for younger children, the IWQOL-Kids was also used for children aged 5–11 in our observational study (parent report under age 7, and child or parent report for ages 7–11), and data of this younger age group was included in the total analysis. A sensitivity analysis for the age group ≥11 years was performed.
The questionnaire consists of 27 items, which can be divided into four subscales: physical comfort, body esteem, social life and family relations. The items were scored on a 5-point scale: 1 = always, 2 = mostly, 3 = sometimes, 4 = rarely, 5 = never. Similarly to the original study [11], the total and subscale scores were calculated as an unweighted sum of scores on the items, followed by transforming these scores on a 0–100 scale. A higher score represents better weight-specific HRQOL.
Due to differences in clinical protocols, the questionnaire used to assess weight-specific HRQOL differed: HELIOS used the IWQOL-Kids child report for all participants [21], LEFF used the IWQOL-Kids parent report for all participants [26], and the protocol for the additional data collection via the webtool varied per location and therapist. As a result, only five paired child and parent report scores were eligible for the IWQOL-Kids. Of these participants, we only included the child report.
The original IWQOL has a high reliability (Cronbach α on total score = 0.96, Cronbach α subscales range 0.88–0.95) and validity [11]. The reliability in our total sample (ages 5–19) was adequate for the total scores (child: α = 0.78, parent α = 0.78) and varied for the subscale scores (child α range: 0.78–0.92, parent α range: 0.67–0.89), with the subscale score for family relations having the lowest reliability (child α: 0.78, parent α: 0.67).
Weight class. Weight class was measured in 0.1 kg and height in 0.1 cm by professionals as part of routine care. Body mass index scores (BMI, kg/m2) were calculated, as were standard deviation scores-BMI (SDS-BMI) scores (BMI corrected for age and sex), according to the Dutch national growth references [29]. Overweight, obesity and severe obesity were based on the international (International Obesity Task Force, IOTF) BMI cut-off points of Cole and Lobstein [30].
Statistical Analyses
Analyses were performed using SPSS version 27. First, the distribution of all continuous baseline and dependent variables was tested. Second, average total, subscale and item scores were calculated for the total group on the PedsQL child report and the IWQOL-Kids child and parent report. While all dependent variables were parametric, mean (SD) scores were reported. Third, for children whose exact weight, height, age and sex were known (N=425), linear regression was used to analyze the association of IOTF BMI class, corrected for age and sex. Fourth, multiple regression analyses with dummy coding of IOTF BMI classes were used to test weight class differences for the total and subscale scores. Fifth, a sensitivity analysis was done to test the robustness of our data: IWQOL-Kids scores for the age group ≥11 years were compared with scores of children aged <11.