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Guttman scale analysis of the distance vision scale
Vijaya K Gothwal1, Thomas A Wright, Ecosse L Lamoureux
1Department of Ophthalmology, National Health and Medical Research Council, Centre for Clinical Eye Research, Flinders University of South Australia, Bedford Park, South Australia, Australia.
Investigative Ophthalmology & Visual Science
|April 17, 2009
Summary
The Distance Vision Scale (DVS) is a valid Guttman scale for assessing vision, but shows a weak correlation with visual acuity. This suggests the DVS measures aspects of vision beyond standard acuity tests.
Area of Science:
- Ophthalmology
- Psychometrics
- Vision Science
Background:
- The Distance Vision Scale (DVS) is a self-assessment tool for visual acuity (VA).
- It is designed with a hierarchical difficulty structure, similar to traditional VA tests.
- Understanding its psychometric properties is crucial for its application.
Purpose of the Study:
- To validate the Distance Vision Scale (DVS) using Guttman scaling criteria.
- To assess the relationship between DVS scores and objective measures of visual acuity (VA) in individuals with cataracts.
Main Methods:
- Guttman analysis was performed on the responses of 108 participants to the DVS.
- Key scalability criteria, including coefficient of reproducibility (CR), minimal marginal reproducibility (MMR), and coefficient of scalability (CS), were evaluated.
- The correlation between DVS total item score and binocular VA was calculated.
Main Results:
- The DVS demonstrated strong evidence of Guttman scalability, with CS=0.93, CR=0.99, and MMR=0.85.
- A statistically significant but weak correlation (r=0.24) was found between the DVS total item score and binocular VA.
- The scale's hierarchical structure was supported by the analysis.
Conclusions:
- The DVS functions as a valid unidimensional and cumulative Guttman scale.
- The poor correlation with VA indicates the DVS captures dimensions of visual performance beyond high-contrast acuity.
- The DVS is suitable for use as an outcome measure for tracking changes and setting treatment goals in vision rehabilitation.
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