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Index of Precision (D)
The index of precision (D) describes that portion of error “contributed by each observation to the average age-class” (Chang 1982). This statistic incorporates the frequency of similar estimates between readers and seems to “credit” the error rate as more readers come up with similar estimates. For example, if 2 readers produced estimates of 23 and 25, X = 24, Average Error (AE)=.04166, and D=.04166. Additional readers repeatedly getting similar results will continue to improve the estimate of error, for example, 4 readers with the estimates of 23, 25, 23, 25, X=24, AE = .04166, but D=.024056.
Literature cited
Chang, W.Y.B. 1982. A statistical method for evaluating the reproducibiliity of age determination.
Canadian Journal of Fisheries and Aquatic Sciences, 39:1208-1210.
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