Description Usage Arguments Value References Examples

View source: R/WelchDegreeOfFreedom.R

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

1 | ```
WelchDegreeOfFreedom(dta, cols, groupingcols)
``` |

`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. |

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

1 2 3 4 5 6 7 8 9 10 | ```
# 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")
``` |

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