Robert has just finished analyzing the results of his 3 x 3 factorial experiment. He examines a line graph that depicts both independent variables on the same axes, and he notes that the lines on the graph are perfectly parallel with each other

Based on this information, what should Robert conclude?

a. There are three main effects in the study.
b. There is an interaction effect in the study.
c. There are nine main effects in the study.
d. There is no interaction effect in the study.

d