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Square Root Transformation of Geographic Atrophy Area Measurements to Eliminate Dependence of Growth Rates on Baseline Lesion Measurements: A Reanalysis of Age-Related Eye Disease Study Report No. 26

William J. Feuer, MS; Zohar Yehoshua, MD, MHA; Giovanni Gregori, PhD; Fernando M. Penha, MD, PhD; Emily Y. Chew, MD; Frederick L. Ferris, MD; Traci E. Clemons, PhD; Anne S. Lindblad, PhD; Philip J. Rosenfeld, MD, PhD
JAMA Ophthalmol. 2013;131(1):110-111. doi:10.1001/jamaophthalmol.2013.572.
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The growth of geographic atrophy (GA) over 4 years in the Age-Related Eye Disease Study (AREDS) was shown to be dependent on the baseline area of GA.1 However, 3 articles have demonstrated that the square root transformation of lesion area measurements eliminates the dependence on baseline lesion size for both the test-retest variability and the growth rates.24 This square root transformation strategy was applied to the AREDS data.

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Figure. Change in area of geographic atrophy using the standard area measurements and the square root transformation of these area measurements. A, Original analysis showing the change in area over 4 years for each of the baseline size categories. B, Revised analysis showing the change in the square root of the area measurements for each of the baseline size categories. DA indicates disc areas.

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