Last modified on Mar 05, 2019

To be able to assess precision requires that protocols be included to maximize precision for estimating ages from scales. These include:

  • Redundancy (more than one reader);
  • Use of ancillary biological data to pinpoint potential errors in scale reads;
  • Use of reference samples and other means of corroboration to improve the readers’ ability to recognize life history characteristics;
    • Corroboration is a measure of the consistency or repeatability of an age estimation method and enables an estimate of precision. To corroborate, means to use multiple age estimation methods to arrive at the same estimate; and
  • Agreement measures include percent agreement (PA), average percent error (APE; Beamish and Fournier 1981), and the coefficient of variation (CV; Chang 1982).


Beamish, R.J. and Fournier, D.A. 1981. A method for comparing the precision of a set of age determinations. Canadian Journal of Fisheries and Aquatic Sciences 38: 982-983.

Chang, W.Y. 1982. A statistical method for evaluating the reproducibility of age determination. Canadian Journal of Fisheries and Aquatic Sciences 39: 1208-1210.