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Eva K. Fenwick, Konrad Pesudovs, Jyoti Khadka, Gwyn Rees, Ecosse Lamoureux; Psychometric Assessment of the Diabetic Retinopathy Module of the Eye-tem Bank Using Rasch Analysis. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5438.
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© ARVO (1962-2015); The Authors (2016-present)
We are developing a diabetic retinopathy (DR) quality of life (QoL) item bank as a disease-specific module of the Eye-tem Bank and we provide a preliminary psychometric report of the DR instrument.
The DR module of the Eye-tem Bank comprises 314 items across 9 QoL domains: Visual symptoms (n=18), Ocular surface symptoms (n=10), Activity limitation (n=120), Mobility (n=19), Emotional (n=48), Health Concerns (n=36), Social (n=21), Convenience (n=30) and Economic (n=12). The items were administered to patients with non-proliferative and proliferative DR; and diabetic macular edema (DME) using face to face and phone interviews. Vision impairment (VI) was defined as none (<6/12), mild (≥6/12-6/18), moderate (>6/18-6/60) and severe (>6/60) in the better eye. Key psychometric properties of each QoL domain were explored using Rasch analysis, including precision (person separation index (PSI) >2.0), unidimensionality (using the principal component analysis of residuals: raw variance explained >50%, unexplained variance by 1st contrast <3.0 eigenvalues and <5.0%), item fit (infit mean square (MNSQ ≤1.5), differential item functioning (DIF contrast <1.0) and measurement range (i.e. hardest to easiest item in logits).
To date, 366 DR/DME patients have completed the pilot items (median age, 62 yrs; range 22-88 yrs) in an average of 52 minutes. Most patients were male (n=253, 69%), not working (n=260, 71%) and had previous laser treatment (n=282, 77%). Of the 366 participants, 199 (54%) had no VI, 77 (21%) had mild VI, 49 (13%) had moderate VI and 24 (7%) had severe VI. Across the 9 QoL domains, only 28 items (8.9%) displayed misfit and only 4 items (1.3%) showed DIF for age or gender. However, the Convenience domain showed evidence of multidimensionality (1st contrast = 4.0 eigenvalues and 5.7%) and 5 domains (Visual symptoms, Ocular surface symptoms, Mobility, Social, Economic) had borderline precision (PSI≤2.0). The average measurement range across the 9 QoL domains was 2.46 logits.
The 9 QoL domains and 314 items in the DR module of the Eye-tem Bank displayed promising psychometric properties. A larger sample covering the breadth of this disease is required to fully evaluate this item bank.
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