WelchDegreeOfFreedom: Welch's rectified degree of freedom

Description Usage Arguments Value References Examples

View source: R/WelchDegreeOfFreedom.R

Description

When variance across groups are heterogeneous, the Student t distribution with n - 1 df is not the exact distribution. However, Welch (1947), using methods of moments, was able to find the best-fitting t distribution. This distribution has degree of freedom reduced based on the sample sizes and the variances of the group tests. The present function returns the rectified degree of freedom

Usage

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WelchDegreeOfFreedom(dta, cols, groupingcols)

Arguments

dta

A data frame containing within-subject measures, one participant per line;

cols

A vector indicating the columns containing the measures.

groupingcols

A vector indicating the columns containing the groups.

Value

df the degrees of freedom rectified according to Welch (1947).

References

\insertAllCited

Examples

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# creates a small data frames with 4 subject's scores for 5 measures:
dta <- data.frame(cbind(
        DV.1 = c(3., 6., 2., 2., 5.),
        DV.2 = c(4., 5., 4., 4., 3.),
        DV.3 = c(2., 7., 7., 8., 6.),
        DV.4 = c(6., 8., 4., 6., 5.),
        grp  = c(1., 1., 2., 2., 2.)
    ))
# performs the test (here rectified df = 1.898876)
WelchDegreeOfFreedom(dta, "DV.1","grp")

superb documentation built on June 23, 2021, 9:08 a.m.