The performance of the UK-English PedsQL™ (age range 8–18 years) was found to be similar to that reported for the original PedsQL™ . We found excellent internal reliability of 0.90 for both self and proxy-report total scales, indicating the suitability of the total scale scores for individual patient analysis . All subscale and summary scores exceeded 0.70, making them acceptable for group comparisons. This is comparable to the reliabilities reported for the original PedsQL™ of 0.88 and 0.90 for self and proxy-report total scales respectively, with all subscale and summary scores also exceeding 0.70.
As with the original PedsQL™, although no floor effects were found the existence of ceiling effects should be noted . Thus whilst the full range of scoring options is used for the majority of subscales, responses tend to be skewed towards the top end of the scale for all subscales, for both self and proxy-report. However, it has been suggested ceiling and floor effects are to be expected in generic HRQL instruments, simply because they aim to be applicable to a wide range of populations . It is possible that the health conditions of the children who took part in the study were well controlled, leading to better HRQL ratings. This issue should be explored further through the administration of PedsQL™ to children with a wider range of health issues including those experiencing acute health problems.
PedsQL™ performed as hypothesized using the known-groups method. There were differences in HRQL between healthy children and those with chronic health conditions for both proxy and self-report. However, children with diabetes scored significantly lower than healthy children on only one dimension – physical functioning. Indeed, they reported better HRQL than children with other chronic health problems and on social and emotional functioning rated their HRQL as better than healthy children, although this did not reach significance. The similarity in HRQL between children with diabetes and their healthy peers has been noted elsewhere . Furthermore, a study into the impact of diabetes screening on adult HRQL reported similarities in HRQL of adults with and without diabetes – both before and after diagnosis . This suggests that the findings of our study are neither atypical nor indicative of a problem with PedsQL™ measurement, but rather represent a meaningful difference in the HRQL of children with diabetes and those with other chronic health problems. Whether this is due to good disease management, the positive support of the diabetes care team or other factors remains unclear. What is apparent however, is that this issue merits further investigation.
Varni et al  did not report any differences in parental or child reporting of HRQL either by age or sex of the child. Whilst this study also found no differences in reporting for the proxy-report, a significant difference in male and female reporting of HRQL was found on the emotional functioning sub-scale of the self-report, with females reporting significantly lower levels of emotional functioning than males. The difference between males and females reflected in our data is consistent with much of the psychological literature concerning gender differences in emotional health [13, 14]. In addition to suggesting that females are more likely to suffer more emotional health problems such as anxiety and depression than males, studies have also proposed that this gender difference is rooted in adolescence [15, 16]. Furthermore, differences in male and female responses to illness have also been suggested, with females more likely to suffer depression following traumatic injury  and to display greater anxiety about chronic illness [18, 19]. Thus the difference in emotional functioning we report here, would seem to reflect a genuine disparity between males and females and so offer further evidence for the validity of PedsQL™ as a sensitive measure of the emotional functioning of children and young people.
Moderate correlation was found between self and proxy-report. The pattern of parent-child correlation for the total sample is similar to that reported for the original PedsQL™, where better correlation was found for physical than for psychological and social functioning . Yet, it should be noted that correlation is better between parents and children where the child has a chronic health condition. Indeed the most marked difference in correlation is on the physical health scale, suggesting that parents and children are more likely to share information about an issue if it is perceived as a problem (in this case physical health). Thus, whilstprevious research has found that parents and children agree more about physical problems, rather than internalising problems such as anxiety or sadness  this may depend in part on whether or not the child has a health problem. Furthermore, it is likely that proxy-reports reflect parental anxiety about their child; in this study parents of children with chronic health problems consistently underestimated their child's HRQL. The limited correlation observed between self and proxy-reports confirms the need to measure both child and parent perspectives when evaluating paediatric HRQL. Furthermore, in situations when the child is unable or unwilling to complete the self-report making it necessary to use a proxy-report to estimate HRQL, the knowledge that this estimate maybe inaccurate should be considered.
A potential limitation of this study is that retest reliability and responsiveness was not conducted. However, it has been argued that test-retest reliability may be less useful than internal consistency reliability in HRQL instrument development . Internal consistency is suggested as a more valuable assessment of the reliability of a measure because of the likelihood of short-term fluctuations in health conditions such as those employed in this study, in which external factors such as disease and treatment variables are known to influence functioning.