Hooded rats: social play times. How does social isolation during a critical developmental period affect the behavior of hooded rats? Psychology students assigned 24 young female rats at random to either isolated or group housing, then similarly assigned 24 young male rats. This is a randomized block design with the gender of the 48 rats as the blocking variable and housing type as the treatment. Later, the students observed the rats at play in a group setting and recorded data on three types of behavior (object play, locomotor play, and social play).8 The data file records the time (in seconds) that each rat devoted to social play during the observation period.

(a) Make a plot of the 4 group means. Is there a large interaction between gender and housing type? Which main effect appears to be more important?

(b) Verify that the conditions for ANOVA inference are satisfied.

(c) Give the complete two-way ANOVA table. What are the F statistics and P-values for interaction and the two main effects? Explain why the test results confirm the tentative conclusions you drew from the plot of means.