12 Checking Assumptions

12.1 Checking Normality Assumptions

Shapiro-Wilk Test

The Shapiro-Wilk test tests the null hypothesis that the samples come from a normal distribution against the alternative hypothesis that the samples do not come from a normal distribution.

shapiro.test(residuals(two_aov))

## 
##  Shapiro-Wilk normality test
## 
## data:  residuals(two_aov)
## W = 0.9634, p-value = 0.6138

QQ Plots

plot(two_aov, 2)

12.2 Checking Homogeneity of Variance Assumption

par(mfrow=c(2,2))
plot(two_aov)

par(mfrow=c(1,1))