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Chung-Jung Chiu, Paul Mitchell, Allen Taylor; Validation of a Composite Scoring System for the Prediction of Advanced Age-related Macular Degeneration. Invest. Ophthalmol. Vis. Sci. 2011;52(14):90.
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Using 5 demographic and 3 ophthalmic predictors in a logistic regression to model result-specific likelihood ratios in the American Age-Related Eye Disease Study (AREDS) dataset (8-y follow-up), we devised a composite (C) scoring system (CAREDS scoring system: CAREDS = -4.48 + ΣCj, AREDS) that permits the prediction of advanced age-related macular degeneration (AMD) (AREDS model in Table 2). The objective of this study is to validate this AREDS model in the Australian Blue Mountains Eye Study (BMES) cohort (10-y follow-up).
To evaluate the performance of the CAREDS scoring system, we first assigned CAREDS score to all eligible eyes in the BMES cohort (Fig 1). Then, at various C score cutoff points each eye was classified into "positive" or "negative" according to its CAREDS score. Next, through frequency table analysis of this classification vs. the actual status of progression to advanced AMD, we calculated the empirical sensitivities/specificities and measured the area under the receiver operating characteristic (ROC) curve (c-indexBMES/AREDS). To explore the deviation of the BMES dataset from the AREDS model, we developed a prediction model (CBMES scoring system) using the BMES dataset as the training sample and compared it to the CAREDS scoring system (Table 2).
The c-indexBMES/AREDS (= 0.921) implies an excellent performance of the CAREDS scoring system in the BMES cohort. However, the empirical sensitivities/specificities deviate from the expected values (Table 1). Although both CAREDS (c-indexAREDS = 0.877) and CBMES (CBMES = -16.26 + ΣCj, BMES, c-indexBMES = 0.953; Fig 2) scoring systems have excellent internal validity, further analysis implies that the deviation is due to the differences in baseline risk factor profile and duration of follow-up between the two cohorts.
These results suggest that, while the methodology of the C scoring system is valid, it will be optimal to use long-term follow-up data from multiple cohorts in order to develop a widely applicable model for the prediction of advanced AMD.
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