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Development and validation of the 21-item children's vision for living scale (CVLS) by Rasch analysis
Kholoud A Bokhary1, Catherine Suttle, Abdullah G Alotaibi
1School of Optometry and Vision Science, University of New South Wales, Sydney, NSW, Australia; Optometry Department, Faculty of Applied Medical Science, King Saud University, Riyadh, Saudi Arabia. optokholoud@hotmail.com.
Background:
The aim was to develop and validate an instrument called the 'Children's Vision for Living Scale' (CVLS) for the assessment of vision-related quality of life in Saudi Arabian children with and without amblyopia.
Methods:
A 43-item child self-report questionnaire was initially developed based on interviews with children with amblyopia, their parents and eye-care professionals, and a literature review. Following a process that involved the removal of redundant items, 28 items remained and were piloted on children aged five to 12 years with and without amblyopia (n = 48 amblyopic, n = 53 non-amblyopic) living in Saudi Arabia. Rasch analysis was applied to determine whether the 28-item questionnaire fitted the Rasch model. Rasch analysis was used to assess the validity and reliability of the questionnaire. Principal components analysis (PCA) was used to check dimensionality. A 21-item questionnaire resulting from this process was administered in children with (n = 81) and without (n = 82) amblyopia in Saudi Arabia for further validation.
Results:
The final 21-item questionnaire had good validity and reliability as demonstrated by person separation of 2.02, person reliability of 0.80 (mean square and standard deviation: infit = 1.01 ± 0.39; outfit = 1.01 ± 0.40) and item reliability of 0.93 (item infit range = 1.33 to 0.78; item outfit range = 0.78 to 1.30). The mean difference between person and item scores of 0.33 ± 0.53 logits (scale range, 2 to -2) indicates that the items are well targeted to the populations. The PCA (dimensionality measures) shows the percentage of variance explained by measures equal to 26.4 per cent (modelled 26.9 per cent) and an eigenvalue of the first contrast of 2.5, which demonstrated good stability.
Conclusion:
The 21-item CVLS is a valid uni-dimensional child self-report instrument for the assessment of the impact of amblyopia on vision-related quality of life in children with and without amblyopia living in Saudi Arabia.
