In this article, we investigated if PedsQL 4.0 was a valid HRQoL scale to assess the impact of ocular conditions on overall health and specific domains such as physical, emotional, social, and school functioning in toddlers (25 to 48 months) and young children (49 to 72 months). We were, however, unable to generate valid scores for any of the latent traits assessed in this study. Most of the responses were considered “extremes” indicating that respondents repeatedly answered that they had “no problem” with the items on the questionnaire. There was almost no variance recorded in this sample. With person separation values approximating 0, the scale demonstrates that it could not discriminate between groups with different levels of the trait being measured. The findings of poor person separation reliabilities were consistent for both aged groups and also those with vision impairment alone (VA <6/12). Combined with poor targeting, disordered thresholds, and evidence of multidimensionality, our findings indicate that the PedsQL 4.0 is not suitable to assess generic overall and associated health domains in this population. Considering the PedsQL 4.0 has never been validated using Rasch analysis, future studies would need to determine if it is psychometrically a suboptimal instrument across all conditions or unsuitable for use in young children with refractive errors.
Our findings contrast with those which have investigated the impact of vision impairment and/or visual field loss in adults using HRQoL scales such as the SF-12,18 SF-36,15,51,52 The WHOQOL,53 EuroQoL (EQ 5D),54,55 and Health Utilities Index Mark 3.56,57 Although disease-specific instruments have shown to be more sensitive to assess the impact of vision loss, several studies have shown a significant relationship between the severity (and/or ocular conditions) and general health status in community living, clinical, or residential care samples. All these investigations, however, have used a classical test theory (CTT) approach to analyze their data. Underpinning CTT is simple scoring of responses to questionnaires; for multi-category response scales, this is usually summary scoring where response categories are assigned ordinal numbers that are summed across questions to arrive at a total score. Whether the findings of these studies would persist using an Item Response Theory method as used in this current investigation would need to be ascertained.
Other factors may also have contributed to the main finding of this study. The initial PedsQL 1.032 was derived from a cancer database and designed as a generic instrument to be used non-categorically across pediatric populations. The validity of the core items was established from healthy children and those with acute or chronic health conditions. Although the authors endeavored to maximize the heterogeneity of the sample during the validation phase, children were recruited from only four hospital speciality clinics namely orthopaedics, cardiology, rheumatology, and diabetes. As such, the non-inclusion of children with sensory impairment in the developmental phases of the PedsQL, may partly explain its unsuitability for use in this population. Another potential contributing factor to the inappropriateness of the PedsQL 4.0 to our sample is the absence of a “Not applicable” response option, which “compelled” the majority of our respondents to choose the option “Not a problem.” This, in turn, contributed to the substantial invariance shown in our data. Contrary to traditional methods of analyzing psychometric data, Rasch analysis is suited to handle missing data because the estimation of a person's latent trait is based on the person's observed item responses. The inclusion of a “Not applicable” option will have informed about items relevant to this population and perhaps generate valid overall and subscales scores for those who have answered relevant items.
The PedsQL 4.0 has been used in previous trials in vision research. Chak and Rahi58 implemented it in children with congenital cataract. The authors concluded that the PedsQL 4.0 was an acceptable instrument for assessing generic HRQoL for children and their parents. Considering that the authors used a CTT approach to analyze their data, caution is warranted about the validity of the authors' concluding statement. A recent study evaluated the impact of presenting visual impairment and refractive errors in an Asian population of adolescent school pupils using the PedsQL 4.0.14 Although the authors used summary scores, they concluded that healthy adolescents with visual impairment experienced statistically although not clinically impaired HRQoL, and refractive errors did not appear to have an impact on QoL. Summary analyses of our data (not shown in our results) would also have indicated that there were no significant associations between those with and without vision loss or ocular conditions on the overall and subscales of the PedsQL 4.0. This finding indicates that the PedsQL 4.0 in its current state is unsuitable for use in toddlers and younger children with vision impairment or refractive errors in an Asian population. It is possible that the questionnaire is not specific or suitable for mild eye disorders such as refractive error. Alternatively it is possible that moderate levels of visual impairment may not significantly impair functional quality of life (or at least the parental perception of it) in children of this age. Further studies are, however, needed to substantiate these hypotheses.
The use of Rasch analysis or other forms of Item Response Theory to analyze patient-centered outcome data has been critically highlighted in this trial. As mentioned earlier, the use of a CTT approach by the study investigators would have concluded that refractive errors have no impact on generic health-related QoL. This would have been an erroneous conclusion as refractive errors may potentially have an impact on QoL but our scale of choice is unsuitable to assess this relationship. In addition to a lack of variance found in the data, the PedsQL 4.0 was also found to display (a) poor targeting, (b) disordered thresholds, and (c) multidimensionality. Therefore, compared with CTT, Rasch analysis provides unparalleled insight into the psychometric properties of questionnaires, including appropriateness of the response categories, measurement precision, unidimensionality, and item fit to the construct. It remains the indispensable statistical technique to analyze questionnaire data.46,59–63
The strengths of this study are its population-based nature and the relatively large sample size. The STARS study was undertaken on a large representative sample of young Singaporean Chinese children who resided in the south western regions of Singapore. The participation rate was 72.3%. The use of Rasch analysis to validate a PedsQL 4.0 scale available in English and Chinese is another strong point of this study. To our knowledge, this is the first time this technique has been used in a population-based survey of eye diseases in toddlers and young children. Conversely, the cross-sectional design is a limitation of this study. Another potential shortcoming is the lack of a prestudy validation phase to test the PedsQL 4.0 using a small sample. However, considering the low prevalence rates of visual impairment or myopia in each age group, it would have taken a similar period of time to collect the data for the prestudy phase as for the main study. In addition, we would have lost the benefits associated with population-based designs. Nonetheless, our study findings are useful in providing directions for future population-based pediatric investigations including our STARS follow-up study.
In conclusion, this study was unable to effectively evaluate the impact of refractive errors on HRQoL in toddlers and young school children in Singapore using the PedsQL 4.0. The scale failed several key psychometric properties of questionnaire validation. Considering that only 3.7 and 2.7% of the toddlers and school children, respectively, had vision impairment, it is possible that their resulting visual disability was of too little magnitude to impact on the current items of the PedsQL 4.0. Future studies could consider if the PedsQL 4.0 can be psychometrically reengineered for use in this population by including additional items. Alternatively, future studies should investigate the development and validation of a disease-specific QoL instrument in very young children with ocular conditions.
We thank the contributions made by the STARS team and the kind participation of all individuals in the STARS project.
The STARS project was supported by the National Medical Research Council (NMRC) NMRC/1009/2005, Singapore, and National HealthCare Group NHG—SIG/07,017, Singapore.
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