ordinalEtaSquared: Eta-squared for ordinal variables

In rcompanion: Functions to Support Extension Education Program Evaluation

Eta-squared for ordinal variables

Description

Calculates eta-squared as an effect size statistic, following a Kruskal-Wallis test, or for a table with one ordinal variable and one nominal variable; confidence intervals by bootstrap.

Usage

ordinalEtaSquared(
  x,
  g = NULL,
  group = "row",
  ci = FALSE,
  conf = 0.95,
  type = "perc",
  R = 1000,
  histogram = FALSE,
  digits = 3,
  reportIncomplete = FALSE,
  ...
)

Arguments

x	Either a two-way table or a two-way matrix. Can also be a vector of observations of an ordinal variable.
g	If x is a vector, g is the vector of observations for the grouping, nominal variable.
group	If x is a table or matrix, group indicates whether the "row" or the "column" variable is the nominal, grouping variable.
ci	If TRUE, returns confidence intervals by bootstrap. May be slow.
conf	The level for the confidence interval.
type	The type of confidence interval to use. Can be any of "norm", "basic", "perc", or "bca". Passed to boot.ci.
R	The number of replications to use for bootstrap.
histogram	If TRUE, produces a histogram of bootstrapped values.
digits	The number of significant digits in the output.
reportIncomplete	If FALSE (the default), NA will be reported in cases where there are instances of the calculation of the statistic failing during the bootstrap procedure.
...	Additional arguments passed to the kruskal.test function.

Details

Eta-squared is used as a measure of association for the Kruskal-Wallis test or for a two-way table with one ordinal and one nominal variable.

Currently, the function makes no provisions for NA values in the data. It is recommended that NAs be removed beforehand.

Because eta-squared is always positive, if type="perc", the confidence interval will never cross zero, and should not be used for statistical inference. However, if type="norm", the confidence interval may cross zero.

When eta-squared is close to 0 or very large, or with small counts in some cells, the confidence intervals determined by this method may not be reliable, or the procedure may fail.

Value

A single statistic, eta-squared. Or a small data frame consisting of eta-squared, and the lower and upper confidence limits.

Author(s)

Salvatore Mangiafico, [e-mail]

References

Cohen, B.H. 2013. Explaining Psychological Statistics, 4th ed. Wiley.

https://rcompanion.org/handbook/F_08.html

See Also

freemanTheta, epsilonSquared

Examples

data(Breakfast)
library(coin)
chisq_test(Breakfast, scores = list("Breakfast" = c(-2, -1, 0, 1, 2)))
ordinalEtaSquared(Breakfast)

data(PoohPiglet)
kruskal.test(Likert ~ Speaker, data = PoohPiglet)
ordinalEtaSquared(x = PoohPiglet$Likert, g = PoohPiglet$Speaker)

### Same data, as matrix of counts
data(PoohPiglet)
XT = xtabs( ~ Speaker + Likert , data = PoohPiglet)
ordinalEtaSquared(XT)

rcompanion documentation built on May 29, 2024, 8:42 a.m.