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Quality Control and Assessment in Aging of Biological Structures
Biologists are taught early the difference between "accuracy" and "precision" in the estimation of parameters.
In age-reading of biological structures, "accuracy" represents the ability to estimate age closest to the true age of the organism.
"Precision" measures the ability to repeat a previous estimate of age.
Without knowing the true age of the organism, scientists are left with only "precision" in assessing the quality of the data.
Precision of data is assessed by rereading part or all of the sample.
Several statistical analyses are commonly used in characterizing the ability to repeat the estimates.
Examples are: average percent error, coefficient of variation, percent agreement, and index of precision.
Some statistics do a better job than others in providing a balanced picture of aging error: "coefficient of variation" may incorporate an aspect of the age range of the sample, while "percent agreement" only describes the portion of the sample which is in agreement.
A graphical depiction of error can be quite useful in quickly seeing trends of one reader vs another.
The ADFG Age Determination Unit routinely tests at minimum 20% of all samples read.
Results from these precision tests are monitored, but are also actively used in improving age data.
If species-specific control limits are transgressed, data are detained for additional evaluation by experienced readers.
Data which fall within control limits are released without additional reading.
Progress of new age readers is tracked using precision test results to monitor their consistency in producing data which falls within acceptable tolerances.
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