A researcher conducted a study looking at how participants' alertness influenced their ability to complete an academic task with, or without coffee. All participants were randomly assigned to either stay up all night or get rest, and subsequently randomly assigned to drink regular coffee or decaffeinated coffee. He finds that there was an interaction between these two factors on the outcome variable. Which of the following is definitely true?
A) With the information provided, there must either be a significant main effect of alertness OR caffeine
B) With the information provided, caffeine and alertness must both be significant main effects
C) With the information provided, neither caffeine nor alertness must necessarily be significant main effects.
D) With the information provided, caffeine and alertness are either both significant main effects, or both not significant main effects.

Question

Quizplus · Accepted Answer

An interaction effect means that the effect of one variable depends on the level of another variable. It does not necessarily imply that either of the variables has a significant main effect on the outcome.

A Researcher Conducted a Study Looking at How Participants' Alertness