R: Friedman Rank Sum Test

friedmanTest {PMCMRplus} | R Documentation

## Friedman Rank Sum Test

### Description

Performs a Friedman rank sum test. The null hypothesis H_0: θ_i = θ_j~~(i \ne j) is tested against the alternative H_{\mathrm{A}}: θ_i \ne θ_j, with at least one inequality beeing strict.

### Usage

    friedmanTest(y, ...)

    ## Default S3 method:
    friedmanTest(y, groups, blocks, dist = c("Chisquare", "FDist"), ...)

### Arguments

`y` | a numeric vector of data values, or a list of numeric data vectors.
`groups` | a vector or factor object giving the group for the corresponding elements of `"x"`. Ignored with a warning if `"x"` is a list.
`blocks` | a vector or factor object giving the block for the corresponding elements of `"x"`. Ignored with a warning if `"x"` is a list.
`dist` | the test distribution. Defaults to `Chisquare`.
`...` | further arguments to be passed to or from methods.

### Details

The function has implemented Friedman's test as well as the extension of Conover anf Iman (1981). Friedman's test statistic is assymptotically chi-squared distributed. Consequently, the default test distribution is `dist = "Chisquare"`.

If `dist = "FDist"` is selected, than the approach of Conover and Imam (1981) is performed. The Friedman Test using the F-distribution leads to the same results as doing an two-way Analysis of Variance without interaction on rank transformed data.

### Value

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

method

  a character string indicating what type of test was performed.

data.name

  a character string giving the name(s) of the data.

statistic

  the estimated quantile of the test statistic.

p.value

  the p-value for the test.

parameter

  the parameters of the test statistic, if any.

alternative

  a character string describing the alternative hypothesis.

estimates

  the estimates, if any.

null.value

  the estimate under the null hypothesis, if any.

### References

Conover, W. J., Iman, R. L. (1981) Rank transformations as a bridge between parametric and nonparametric statistics, The American Statistician 35, 124–129.

Sachs, L. (1997) Angewandte Statistik. Berlin: Springer.

### See Also

`friedman.test`

### Examples

    ## Hollander & Wolfe (1973), p. 140ff.
    ## Comparison of three methods ("round out", "narrow angle", and
    ##  "wide angle") for rounding first base.  For each of 18 players
    ##  and the three method, the average time of two runs from a point on
    ##  the first base line 35ft from home plate to a point 15ft short of
    ##  second base is recorded.
    RoundingTimes <-
    matrix(c(5.40, 5.50, 5.55,
            5.85, 5.70, 5.75,
            5.20, 5.60, 5.50,
            5.55, 5.50, 5.40,
            5.90, 5.85, 5.70,
            5.45, 5.55, 5.60,
            5.40, 5.40, 5.35,
            5.45, 5.50, 5.35,
            5.25, 5.15, 5.00,
            5.85, 5.80, 5.70,
            5.25, 5.20, 5.10,
            5.65, 5.55, 5.45,
            5.60, 5.35, 5.45,
            5.05, 5.00, 4.95,
            5.50, 5.50, 5.40,
            5.45, 5.55, 5.50,
            5.55, 5.55, 5.35,
            5.45, 5.50, 5.55,
            5.50, 5.45, 5.25,
            5.65, 5.60, 5.40,
            5.70, 5.65, 5.55,
            6.30, 6.30, 6.25),
          nrow = 22,
          byrow = TRUE,
          dimnames = list(1 : 22,
                          c("Round Out", "Narrow Angle", "Wide Angle")))

    ## Chisquare distribution
    friedmanTest(RoundingTimes)

    ## check with friedman.test from R stats
    friedman.test(RoundingTimes)

    ## F-distribution
    friedmanTest(RoundingTimes, dist = "FDist")

    ## Check with One-way repeated measure ANOVA
    rmat <- RoundingTimes
    for (i in 1:length(RoundingTimes[,1])) rmat[i,] <- rank(rmat[i,])
    dataf <- data.frame(
        y = y <- as.vector(rmat),
        g = g <- factor(c(col(RoundingTimes))),
        b = b <- factor(c(row(RoundingTimes))))
    summary(aov(y ~ g + Error(b), data = dataf))

[Package PMCMRplus version 1.6.1 Index]