A novel driving scale for adults experiencing amblyopia and/or strabismus: Psychometric evaluation by Rasch analysis

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Kumaran, Sheela
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Flinders University
Aim: To evaluate the psychometric properties of a novel driving scale for adults experiencing amblyopia and/or strabismus using Rasch measurement theory. Background: To develop item banks that measure quality of life dimensions, important to adults with amblyopia and/or strabismus, an extensive qualitative study was conducted in Australia and India. Among other findings, the study identified several impacts in driving, which were articulated into country-specific surveys by item refinement and revision processes. This abstract presents the psychometric validation of this scale for the Indian population. Methods: The 18-item driving scale was administered to adults in India, aged over 18 years. Rasch analysis (using Winsteps version 3.92.1) was used to assess the psychometric properties of the scale: functioning of response categories, measurement precision (PSI), fit statistics, dimensionality, targeting and differential item functioning (DIF). Results: Two hundred and thirty two participants (male: 72%, median age: 24 year; range: 18-48 years) completed the survey. The scale had a PSI of 2.44. Two misfit items were fixed by iteratively muting erroneous person responses to each item. Variance explained by the measure was 64%. The eigen value was 2.98 and 5 items loaded over 0.40; however the disattenuated correlations between the item clusters was >0.80, indicating that the items are measuring the same thing. This was further verified by splitting the scale into two and correlating person measures (spearman correlation = 0.78; 61% of the variance was shared by the measures). The final scale had ordered thresholds, PSI, 2.52 and targeting, 2.51 logits. Two items showed notable DIF based on ocular diagnosis. Conclusion: The 18-item driving scale displays valid Rasch- based psychometric properties except for targeting. Implications: The Rasch validated driving scale could be used to measure and compare driving abilities of individuals with amblyopia and/or strabismus.
This abstract was prepared for the inaugural 'HDR Student Conference', Flinders University, November 2018. Copyright © the author
Driving, Amblyopia, Strabismus, Rasch analysis, Psychometrics
Kumaran, Sheela (2018, November) A novel driving scale for adults experiencing amblyopia and/or strabismus: Psychometric evaluation by Rasch analysis Paper presented at 'HDR Student conference', Flinders University, Bedford Park.