CV.test: Coefficient of Variation Test

In kmiddleton/zar5: Data sets from Biostatistical Analysis

Description

Coefficient of Variation Test

Usage

CV.test(x1, x2, test = "F")

Arguments

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.

Details

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.

Value

CV1, CV2	Coefficients of variation for x1 and x2. If test = "F", the coefficients of variation are reported in the original (non-log-transformed) units.
test	The type of test performed, "F" or "Z"
test.stat	The test statistic for test
p	P-value for the test statistic

Author(s)

Kevin Middleton ([e-mail])

References

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

Examples

Weight <- ex08.08$Weight
Height <- ex08.08$Height
CV.test(Weight, Height, test = "F")
CV.test(Weight, Height, test = "Z")

kmiddleton/zar5 documentation built on May 20, 2019, 12:51 p.m.