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D. R. Tabrett, K. Latham; Using Rasch Analysis to Refine the Nottingham Adjustment Scale (NAS) in the Visually Impaired. Invest. Ophthalmol. Vis. Sci. 2010;51(13):940.
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© ARVO (1962-2015); The Authors (2016-present)
The Nottingham Adjustment Scale (NAS) 1 is an existing self-report instrument that attempts to assess the degree of adjustment to visual impairment. Some of its psychometric properties have been tested previously; this study evaluates the NAS using Rasch analysis in a sample of visually impaired adults.
The original 55-item NAS was administered to 62 individuals with visual impairment during face to face interviews. Habitual binocular distance visual acuity (VA) was measured as was the level of depressive symptoms using the Geriatric Depression Scale (GDS). Using Rasch analysis, a revised instrument was developed. The properties of the revised instrument were then explored.
Response scale and item function were sub-optimal in the original NAS. Performance was improved by altering the response scale and conducting systematic item reduction. The revised 28-item NAS has high person (0.87) and item (0.94) reliabilities and a person separation of 2.57. Items were better targeted to the less well-adjusted in this sample. Person measures derived from the revised NAS did not correlate with VA (r=-0.16, p=.20) and correlated moderately with GDS scores (r=0.73; p<.001), indicating good discriminant and convergent validity, respectively.Conclusions: The NAS instrument can be improved by editing the response scale and removing misfitting items. The resultant 28-item instrument is a reliable and valid measure of adjustment to vision loss in this visually impaired study sample. Scale function may be improved further by the formulation of items targeted towards the better adjusted.
1. Dodds AG, et al., J Vis Imp Blindness 1991;85:306-310.
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