Bowman, D.T.
(2001)
Common Use of the CV: A Statistical Aberration in Crop Performance Trials (Contemporary Issue).
Journal of Cotton Science, 5 (2).
pp. 137-141.
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Abstract
The coefficient of variation (CV) was created to
measure population variability. However, its most
common use is to measure validity of field
experiments. The CV can be used to measure
variability in genetic populations, to determine the
best plot size in uniformity trials, to measure
stability of phenotypes, or measure variation in
other individual or population attributes. The CV is
based on the assumption that the mean and the
error variance change together such that regressing
the natural log of error variance on the natural log
of the mean produces a β = 2.0. Twenty-two sets of
crop performance data revealed no relationship
approaching β = 2.0. Thus, there is no basis for using
the CV for crop performance trials. If concern exists
about heterogeneity of error variances, the data
could be transformed on the basis of the
relationship between the error and mean for that
crop. Locations with higher yield have a larger
impact on overall means than locations with lower
yield, but one could minimize that impact by
calculating relative yield. The CV should no longer
be used to indicate validity in most field trials,
particularly crop performance trials.
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