You are concerned with college drinking behavior.

You think it is related to your year in school.

You collect data from 1st year, Sophomores, and Juniors.
For this example, I don't care about Seniors.

Thus, Year will be factor A with 3 levels = A1, A2, A3

You think it is also related to gender.

Thus, Gender will be factor B with 2 levels = B1, B2

You calculate the means.

What questions can we answer?

• Do the Years differ? This is the Main Effect of Year - Factor A!
• Do the Genders differ? This is the Main Effect of Gender - Factor B!
• Does the pattern of the differences between years depend on Gender? This is the Interaction of Year by Gender - the AB interaction!