I've been using var.test and bartlett.test to check basic ANOVA assumptions, among others, homoscedascity (homogeniety, equality of variances). Procedure is quite simple for... moreI've been using var.test and bartlett.test to check basic ANOVA assumptions, among others, homoscedascity (homogeniety, equality of variances). Procedure is quite simple for One-Way ANOVA:
bartlett.test(x ~ g) # where x is numeric, and g is a factor
var.test(x ~ g)
But, for 2x2 tables, i.e. Two-Way ANOVA's, I want to do something like this:
bartlett.test(x ~ c(g1, g2)) # or with list; see latter:
var.test(x ~ list(g1, g2))
Of course, ANOVA assumptions can be checked with graphical procedures, but what about "an arithmetic option"? Is that, at all, manageable? How do you test homoscedascity in Two-Way ANOVA?