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P. M. O'Connor, B. C. Scarr, E. L. Lamoureux, R. T. Le Mesurier, J. E. Keeffe; Adaptation and Validation of a Quality of Life Questionnaire for Use in the Pacific Islands. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3147. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To adapt the Impact of Vision Impairment (IVI) questionnaire for use in Pacific island countries.
Following in-depth interviews (n=24) and a pilot study (n=67), the questionnaire was translated, adapted and the Melanesian IVI (IVI_M) administered to 189 participants in the Pacific nation, Vanuatu. The instrument was tested for face, content and construct validity. Structural validity was assessed using Principal Components Analysis (PCA) and Rasch analysis to validate the scale.
86% of the original 28 item IVI were deemed relevant by >90% of the participants of the pilot study. Four items displaying floor effects or significant high Spearman’s correlations were removed, 2 were combined and 3 items were rephrased to reflect activities unique to Melanesian society. 19 core items were found to be relevant to both the Australian and Melanesian contexts. However, items related to reading were irrelevant to the Vanuatu participants. The final 23 item IVI_M was then tested for content and structural validity. The Cronbach alpha for the draft instrument was 0.853, indicating good homogeneity. Test-retest and inter-observer intraclass correlation coefficients >0.9 demonstrated substantial reliability. PCA indicated two domains: ‘emotional wellbeing’ and ‘mobility and activities of daily living’. Initial application of the data to the Rasch model showed a lack of fit and disordered thresholds were observed. Category collapsing were undertaken which produced an overall fit to the Rasch model (item-trait interaction X2 = 58.7, p=0.07). Person Separation Reliability was high (0.92). All items were found to be free from DIF (gender, level of visual acuity, location) and unidimensionality was confirmed. ‘Safety outside of the home’ ranked as the least difficult item of the Rasch-calibrated IVI_M (-1.4 logit) while ‘interference with life’ ranked most difficult (1.9 logit).
The IVI_M was found to be a culturally appropriate, valid and reliable quality of life questionnaire for use in Pacific Island countries. The instrument could be used to determine the impact of vision impairment and evaluate eye care intervention programs in this region of the world.
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