tukeySEM {semTools}

Tukey's WSD post-hoc test of means for unequal variance and sample size

Description

This function computes Tukey's WSD post hoc test of means when variances and sample sizes are not equal across groups. It can be used as a post hoc test when comparing latent means in multiple group SEM.

Usage

tukeySEM(m1, m2, var1, var2, n1, n2, ng)

Arguments

m1

Mean of group 1.

m2

Mean of group 2.

var1

Variance of group 1.

var2

Variance of group 2.

n1

Sample size of group 1.

n2

Sample size of group 2.

ng

Total number of groups to be compared (i.e., the number of groups compared in the omnibus test).

Details

After conducting an omnibus test of means across three of more groups, researchers often wish to know which sets of means differ at a particular Type I error rate. Tukey's WSD test holds the error rate stable across multiple comparisons of means. This function implements an adaptation of Tukey's WSD test from Maxwell & Delaney (2004), that allows variances and sample sizes to differ across groups.

Value

A vector with three elements:

1. q: The q statistic

2. df: The degrees of freedom for the q statistic

3. p: A p value based on the q statistic, df, and the total number of groups to be compared

Author(s)

Alexander M. Schoemann (East Carolina University; [e-mail])

References

Maxwell, S. E., & Delaney, H. D. (2004). Designing experiments and analyzing data: A model comparison perspective (2nd ed.). Mahwah, NJ: Lawrence Erlbaum Associates.

Examples

## For a case where three groups have been compared:
## Group 1: mean = 3.91, var = 0.46, n = 246
## Group 2: mean = 3.96, var = 0.62, n = 465
## Group 3: mean = 2.94, var = 1.07, n = 64

## compare group 1 and group 2
tukeySEM(3.91, 3.96, 0.46, 0.62, 246, 425, 3)

## compare group 1 and group 3
tukeySEM(3.91, 2.94, 0.46, 1.07, 246, 64, 3)

## compare group 2 and group 3
tukeySEM(3.96, 2.94, 0.62, 1.07, 465, 64, 3)