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Graphical Depiction of Error ~ Age Bias Plots
Age bias plots (Campana et al 1995) are one of the easiest and visual ways to quickly assess error. They plot one set of estimates against another, showing trends throughout the age range of the sample. For example, APE or CV describe general error within the sample. Age bias plots may suggest trends in this error: higher error in the younger fish vs older, underaging or overaging between readers. They are an excellent complement to any age-reading quality control program.
Literature cited
Campana, S.E., M.C. Annand, and J. I. McMillan. 1995. Graphical and statistical methods for determining the consistency of age determinations. Transaction of the American Fisheries Society 124:131-138..
Figure 1. An age bias plot showing relatively consistent error throughout the age range. The line represents perfect agreement.
Figure 2. These data show fair agreement between Reader 1 and 2 up to age 9, but a trend of younger ages by Reader 2.
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