WRS2: t2way – R documentation

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t2way

A two-way ANOVA for trimmed means, M-estimators, and medians.

Description

The t2way function computes a two-way ANOVA for trimmed means with interactions effects. Corresponding post hoc tests are in mcp2atm. pbad2way performs a two-way ANOVA using M-estimators for location with mcp2a for post hoc tests.

Usage

t2way(formula, data, tr = 0.2)
pbad2way(formula, data, est = "mom", nboot = 599, pro.dis = FALSE)
mcp2atm(formula, data, tr = 0.2)
mcp2a(formula, data, est = "mom", nboot = 599)

Arguments

`formula`	an object of class formula.
`data`	an optional data frame for the input data.
`tr`	trim level for the mean.
`est`	Estimate to be used for the group comparisons: either `"onestep"` for one-step M-estimator of location using Huber's Psi, `"mom"` for the modified one-step (MOM) estimator of location based on Huber's Psi, or `"median"`.
`nboot`	number of bootstrap samples.
`pro.dis`	If `FALSE`, Mahalanobis distances are used; if `TRUE` projection distances are computed.

Details

t2way does not report any degrees of freedom since an adjusted critical value is used. pbad2way returns p-values only; if it happens that the variance-covariance matrix in the Mahalanobis distance computation is singular, it is suggested to use the projection distances by setting pro.dis = TRUE.

Value

The functions t2way and pbad2way return an object of class t2way containing:

`Qa`	first main effect
`A.p.value`	p-value first main effect
`Qb`	second main effect
`B.p.value`	p-value second main effect
`Qab`	interaction effect
`AB.p.value`	p-value interaction effect
`call`	function call
`varnames`	variable names
`dim`	design dimensions

The functions mcp2atm and mcp2a return an object of class mcp containing:

`effects`	list with post hoc comparisons for all effects
`contrasts`	design matrix

References

Wilcox, R. (2012). Introduction to Robust Estimation and Hypothesis Testing (3rd ed.). Elsevier.

Examples

## 2-way ANOVA on trimmed means
t2way(attractiveness ~ gender*alcohol, data = goggles)

## post hoc tests
mcp2atm(attractiveness ~ gender*alcohol, data = goggles)

## 2-way ANOVA on MOM estimator
pbad2way(attractiveness ~ gender*alcohol, data = goggles)

## post hoc tests
mcp2a(attractiveness ~ gender*alcohol, data = goggles)

## 2-way ANOVA on medians
pbad2way(attractiveness ~ gender*alcohol, data = goggles, est = "median")

## post hoc tests
mcp2a(attractiveness ~ gender*alcohol, data = goggles, est = "median")

## extract design matrix
model.matrix(mcp2a(attractiveness ~ gender*alcohol, data = goggles, est = "median"))

WRS2

A Collection of Robust Statistical Methods

v1.1-1

GPL-3

Authors

Patrick Mair [cre, aut], Rand Wilcox [aut]

Initial release

2021-02-09