Description Usage Arguments Details Value Author(s) References Examples
Coefficient of Variation Test
1 | CV.test(x1, x2, test = "F")
|
x1 |
a numeric vector |
x2 |
a numeric vector |
test |
the type of test to perform, "F" for a variance-ratio test or "Z" for a Z test. |
CV.test
tests for the difference in coefficients of variations for
two variables (x1
and x2
), using either a variance ratio
(F) test (default) or a Z test.
The variance-ratio test was described by Lewontin (1966), but apparently dates back to Wright (1952) and Bader and Lehman (1965). This test involves a ratio of log-transformed variances, which follows an F-distribution with n1-1 and n2-1 degrees of freedom.
Miller (1991) describes a Z test that does not involve a log-transformation, provided that the data are positive and normally distributed. The Z test performs best if the coefficients of variation are less than 0.33.
CV1, CV2 |
Coefficients of variation for |
test |
The type of test performed, "F" or "Z" |
test.stat |
The test statistic for |
p |
P-value for the test statistic |
Kevin Middleton (middletonk@missouri.edu)
Bader, R.S. and W.H. Lehman. 1965. Phenotypic and genotypic variation in odontometric traits of the house mouse. American Midlands Naturalist 74: 28-38.
Lewontin, R.C. 1966. On the measurement of relative variability. Systematic Zoology 15: 141-142. http://www.jstor.org/stable/2411632
Miller, G.E. 1991. Asymptotic test statistics for coefficients of variation. Communications in Statistics-Theory and Methods 20: 2251-2262.
Wright, S. 1952. The genetics of quantitative variability. In: Reeve, E.C.R. and C. Waddington (eds.). Quantitative Inheritance. pp. 5-41. H.M.S.O., London.
Zar, J.H. 2010. Biostatistical Analysis. 5th Edition. Pearson Prentice-Hall. Upper Saddle River, NJ. ISBN-10: 0131008463. ISBN-13: 978013100846. http://www.pearsonhighered.com/educator/product/Biostatistical-Analysis/9780131008465.page
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