1. Population
We included 220 children, of which 123 CHD and 97 controls. Among them, 210 children (117 CHD and 93 controls) completed the PedsQL self-questionnaire and 220 parents completed the PedsQL proxy-questionnaire.
Median age was 10 years (interquartile range 9-11 years), and 60% of children were boys. In the CHD group, severity class 1, 2, 3 and 4 concerned, respectively, 33 (27%), 14 (11%), 62 (50%) and 11 (9%) children.
2. Psychometric validation
2.1. Reliability
Test-retest analyses showed that ICCs, overall and in each dimension, for both self and proxy reports, were in the range of 0.49 to 0.66, corresponding to moderate (0.41-0.6) to good agreement (0.6-0.8) (Table 1).
2.2. Validity
2.2.1. Face validity and Content validity
Face validity index was excellent in the parents’ group (0.85) and very good in the children group (0.75). However, for many children did not fully understand the meaning of item 4 (“it is hard for me to lift something heavy”), as most of them understood the question from a general perspective and not as a limitation potentially related to their health condition. During the interview, most children reported that “yes, it is hard for a child to lift something heavy, as compared to an adult”. Similarly, item 20 (“I forget things”) was frequently misunderstood, and two possible meanings were given for parents and children: forgetting concepts, lessons, or words during the class, or forgetting to bring an object to school (notebook, pencil case).
Content validity index was good (0.7). However, the experts considered that item 1 was not adapted to children living in the countryside (“It is hard for me to walk more than one block”). Moreover, item 4 (“It is hard for me to lift something heavy”) was often misinterpreted as mentioned before, and item 23 (“I miss school to go to the doctor or hospital”) was usually understood from a general perspective: both healthy and CHD children miss school to go to the doctor, but sick children may miss school more often than healthy subjects, which was not always interpreted this way.
2.2.2. Criterion validity
In terms of concurrent validity, PedsQL and Kidscreen corresponding dimensions correlated well in physical (r=0.57), emotion (r=0.49 with psychological well-being, 0.50 with moods and emotions, and 0.48 with self perception of the Kidscreen) and school dimensions (r=0.41) for self-report (Table 2). For parents’ reports, these correlations were good in physical (r=0.48), psychological (r=0.57), and school (r=0.49) dimensions. Indeed, the highest correlations observed between both instruments were those expected, except for social dimension. For the PedsQL social dimension, only one of the three corresponding dimensions of the Kidscreen (“bullying”) had a close-to-high correlation (r=0.47). For parents reports, the social PedsQL dimension correlated better with the school dimension than with the two expected dimensions of the Kidscreen (“autonomy & parents relation” and “social support & peers”).
2.2.3. Construct validity
2.2.3.1. Structural validity
(i)Redundancy between items
In the PedsQL self-reports, none of the items had correlation coefficients above 0.70 for each dimension. In the proxy reports, high correlations were found between items 2-running and 3-sports (r=0.90, P<0.001), and between items 19-attention and 21-schoolwork (r=0.71, P<0.001). All remaining items from the proxy reports had correlation coefficients <0.70.
(ii) Item-internal consistency (IIC)
Most correlations between items and the corresponding dimension were ≥0.4 (Supplementary Table 1). Lower correlations were found for item 5-bath, 6-chores and 7-aches of the physical dimension (self-reports only), for item 17-doing-things of the social dimension for controls (self and proxy reports), and for item 22-feeling-well and 23-doctor of the school dimension for both CHD and control children.
(iii) Item discriminant validity
In most cases, items correlated more with their own dimention than with other dimensions (Supplementary Table 1). However, a few items better correlated with other dimensions, but with rather close correlation coefficients.
(iv) Variability of items
Among CHD children, all items had a coefficient of variation above 20%, except item 5-bath, in self-reports only. Among control children, self-reports showed coefficients of variation <20% for item 1-walking, 3-sports and 5-bath, and for item 18-playing. Parent-reports yielded coefficients of variation <20% for item 17-doing-things, and items 22-not-feeling-well and 23-doctor.
(v) Internal consistency
In all 4 dimensions, Cronbach alpha coefficients were ≥0.69 (Table 1). Cronbach alpha coefficients for each dimension did not increase after removal of each item one by one.
(vi) Factor analysis
The goodness-of-fit statistics of the confirmatory factor analysis rejected the original structure with 4 factors (for self-reports : p χ² <0.0001, AGFI=0.698, RMSEA=0.100 [0.092 ;0.109]90%, CFI=0.731, and SRMR=0.089; and for proxy reports : p χ² <0.0001, AGFI=0.611, RMSEA=0.120 [0.112 ;0.128]90%, CFI=0.724, and SRMR=0.125. For both reports, p χ² were <0.05, RMSEA and SRMR were <0.08, and AGFI and CFI were <0.90, showing no adequate fit model.
In the exploratory factor analysis, for self and proxy reports, only 2 factors were retained according to scree test and parallel analysis (Supplementary Figure 1), corresponding to physical (factor 1) and psychological (factor 2) dimensions. The factor loadings matrix and the variance explained by each factor were reported in Table 3.
In the PedsQL self-questionnaire, factor 1 included all items from the physical dimension, except one item (item 7-aches), and also included some items from the social dimension that could be interpreted by children as physical actions (items 17-doing-things and 18-playing), as well as two items from the school dimension, referring to somatic problems (items 22-not-feeling-well and 23-doctor). In the PedsQL proxy-questionnaire, factor 1 included all items of the physical dimension, but two items (items 7-aches and 8-energy), which were considered as belonging to the psycho-social domain.
The factor 2, in both self and proxy-questionnaires, included most items in a psycho-social domain grouping psychological, emotion, social and school dimensions (Table 3).
In the 4-factor loadings analysis, most items of the self-questionnaire were grouped in factor 1 for the physical dimension, factor 2 for the emotional and social dimensions, and factor 4 for the school dimension. As the proxy-questionnaire, most items could be grouped in factor 1 for the physical dimension, factor 2 for the emotional dimensions, factor 3 for the social dimension, and factor 4 for the school dimension (supplementary Table 2).
2.2.3.2. Hypothesis testing
The original physical dimension of the PedsQL moderately correlated with physical capacity, as assessed by the VO2max, in both self-reports (r=0.22, P=0.08) and proxy reports (r=0.35, P=0.01). In the same patients, the correlations between the physical dimension of the Kidscreen and the VO2max were even lower in both self-reports (r=0.19, P=0.16) and proxy reports (r=0.25, P=0.05).
2.4. Interpretability
2.4.1. Acceptability and quality of items
Among the 210 children who completed the PedsQL self-questionnaire, 98% had no missing items. As for the PedsQL proxy questionnaires, 213 of 220 parents (97%) had no missing items. Missing data did not relate to any specific item. Ceiling effect exceeded 20% for the social dimension (self and proxy reports for CHD and control children) and physical dimension (self-reports for CHD children and self and proxy reports for controls) (Table 1). Floor effect was 0% for all dimensions in both groups. At the item level, a high ceiling effect (≥80%) was observed for item 1-walking and item 5-bath of the physical dimension in CHD and control self and parent-reports, and in item 18-playing of the social dimension for control self-reports only. No significant floor effect was observed.
2.4.2. Discriminant validity
PedsQL self-reported scores were significantly lower in CHD children than in controls in all dimensions (Table 1). Effect size was medium for school, physical, psychosocial and total scores, and small for emotion and social scores. Parents-reported scores were lower for CHD patients in all dimension except the social one, with small effect sizes.
Differences in PedsQL scores by gender and CHD severity were reported in Table 4. Female self-reported HR-QoL scores were lower than male’s scores for emotional, physical, and total scores. No difference was observed between boys and girls according to parents-reports. PedsQL self-reports were significantly different in terms of CHD severity for physical, social, psychosocial and total scores. PedsQL proxy-reports were significantly different in terms of CHD severity for physical, social, and total scores. The ability to discrimate CHD severity with the PedsQL was mainly observed, for both self and proxy questionnaires, between the low severity class (class 1) and the three other severity classes (2, 3 and 4), but not between the 2 intermediate severity classes (2 and 3).