ks.gof: Kolmogorov-Smirnov test

Description

Performs one or two sample Kolmogorov-Smirnov tests.

Usage

ks.gof(x, y, ..., alternative = c("two.sided", "less", "greater"), 
exact = NULL)

Value

A list with class "htest" containing the following components:

statistic: Value of test statistics.
p.value: P-value.
alternative: Character string describing the alternative hypothesis.
method: Character string indicating what type of test was performed.
data.name: Character string giving the name(s) of the data.

Arguments

x: A numeric vector of data values.
y: Either a numeric vector of data values, or a character string naming a distribution function.
...: Parameters of the distribution specified (as a character string) by 'y'.
alternative: Indicates the alternative hypothesis and must be one of "two.sided" (default),"less", or "greater". You can specify just the initial letter.
exact: NULL or a logical indicating whether an exact p-value should be computed. See Details for the meaning of NULL. Not used for the one-sided two-sample case.

Author

Details

If y is numeric, a two-sample test of the null hypothesis that x and y were drawn from the same continuous distribution is performed.

Alternatively, y can be a character string naming a continuous distribution function. In this case, a one-sample test is carried out of the null that the distribution function which generated x is distribution y with parameters specified by "...".

The possible values "two.sided" (default),"less" and "greater" of alternative specify the null hypothesis that the true distribution function of x is equal to, not less than or not greater than the hypothesized distribution function (one-sample case) or the distribution function of y (two-sample case), respectively.

Exact p-values are not available for the one-sided two-sample case, or in the case of ties. exact = NULL (the default), an exact p-value is computed if the sample size if less than 100 in the one-sample case, and if the product of the sample sizes is less than 10000 in the two-sample case. Otherwise, asymptotic distributions are used whose approximations may be inaccurate in small samples. In the one-sample two-sided case, exact p-values are obtained as described in Marsaglia, Tsang & Wang (2003). The formula of Birnbaum & Tingey (1951) is used for the one-sample one-sided case.

If a single-sample test is used, the parameters specified in "..." must be pre-specified and not estimated from the data. There is some more refined distribution theory for the KS test with estimated parameters (see Durbin, 1973), but that is not implemented in ks.gof.

References

Z. W. Birnbaum & Fred H. Tingey (1951), One-sided confidence contours for probability distribution functions. The Annals of Mathematical Statistics, *22*/4, 592-596.

William J. Conover (1971), Practical nonparametric statistics. New York: John Wiley & Sons. Pages 295-301 (one-sample "Kolmogorov" test), 309-314 (two-sample "Smirnov" test).

Durbin, J. (1973) Distribution theory for tests based on the sample distribution function. SIAM.

George Marsaglia, Wai Wan Tsang & Jingbo Wang (2003), Evaluating Kolmogorov's distribution. Journal of Statistical Software, *8*/18. <URL: http://www.jstatsoft.org/v08/i18/>.

Examples

Run this code

x <- rnorm(50)
y <- runif(30)
# Do x and y come from the same distribution?
ks.gof(x, y)
# Does x come from a shifted gamma distribution with shape 3 and rate 2?
ks.gof(x+2, "pgamma", 3, 2) # two-sided, exact
ks.gof(x+2, "pgamma", 3, 2, exact = FALSE)
ks.gof(x+2, "pgamma", 3, 2, alternative = "gr")

Run the code above in your browser using DataLab