27.9 Arguments:

• k: Number of groups
• n: Number of observations (per group)
• f: Effect size
• sig.level: Significance level (Type I error probability)
• power: Power of test (1 minus Type II error probability)

$$f = \sqrt{\frac{σ²ₘ}{σ²}}$$ Where $σ²ₘ$ is the variation of the group means and $σ²$ is the average variation within groups (Each typically estimated).

Suggested interpretation: (this is not likely discipline appropriate):

• $f=0.10$ is a small effect
• $f=0.25$ is a medium effect
• $f=0.40$ is a large effect