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Andhra Pradesh Eye Disease Study - Visual Function Questionnaire: further improvements in psychometric properties
Vijaya K Gothwal1, Deepak K Bagga
1Meera and L B Deshpande Centre for Sight Enhancement, Vision Rehabilitation Centres, L V Prasad Eye Institute, Hyderabad, India. vijayagothwal@gmail.com
Ophthalmic Epidemiology
|September 18, 2012
Summary
The Andhra Pradesh Eye Disease Study-Visual Function Questionnaire (APEDS-VFQ) precisely measures visual ability in visually impaired Indian adults. Visual ability is a two-factor construct, with one factor impacting reading and the other mobility.
Area of Science:
- Ophthalmology
- Psychometrics
- Biostatistics
Background:
- The Andhra Pradesh Eye Disease Study-Visual Function Questionnaire (APEDS-VFQ) is used to assess visual function.
- Previous Rasch analysis of the APEDS-VFQ was not comprehensive, particularly regarding its dimensionality.
Purpose of the Study:
- To conduct a detailed psychometric assessment of the APEDS-VFQ using Rasch analysis.
- To evaluate the dimensionality and construct validity of the APEDS-VFQ in visually impaired adults.
Main Methods:
- Rasch analysis was applied to data from 351 visually impaired adults verbally administered the APEDS-VFQ.
- Response categories were reduced from five to three due to limited participant discrimination.
- Items were analyzed for fit, and dimensionality was assessed through principal component analysis.
Main Results:
- The APEDS-VFQ demonstrated good overall fit, with one item showing misfit.
- The underlying construct of visual ability was found to be multidimensional, not unidimensional.
- A two-factor structure emerged, with distinct dimensions influencing reading and peripheral vision (mobility).
- High reliability was observed for both item (0.99) and person (0.81) separation.
Conclusions:
- The APEDS-VFQ is a precise and reliable measure of visual ability in visually impaired adults in India.
- Visual ability is a two-factor latent variable, aligning with findings from Western visual function questionnaires.
- The questionnaire effectively differentiates between visual abilities related to reading and mobility.
