14.2 4 Steps to conduct an ANOVA

Here are the 4 steps you should follow to conduct a standard ANOVA in R:

1. Create an ANOVA object using the aov() function. In the aov() function, specify the independent and dependent variable(s) with a formula with the format y ~ x1 + x2 where y is the dependent variable, and x1, x2 … are one (more more) factor independent variables.

# Step 1: Create an aov object
mod.aov <- aov(formula = y ~ x1 + x2 + ...,
               data = data)

2. Create a summary ANOVA table by applying the summary() function to the ANOVA object you created in Step 1.

# Step 2: Look at a summary of the aov object
summary(mod.aov)

3. If necessary, calculate post-hoc tests by applying a post-hoc testing function like TukeyHSD() to the ANOVA object you created in Step 1.

# Step 3: Calculate post-hoc tests
TukeyHSD(mod.aov)

4. If necessary, interpret the nature of the group differences by creating a linear regression object using lm() using the same arguments you used in the aov() function in Step 1.

# Step 4: Look at coefficients
mod.lm <- lm(formula = y ~ x1 + x2 + ...,
             data = data)

summary(mod.lm)