An investigator randomly assigns 30 college students into three equal size study groups (early- morning, afternoon, late-night) to determine if the period of the day at which people study has an effect on their retention. The students live in a controlled environment for one week, on the third day of the experimental treatment is administered (study of predetermined material). On the seventh day the investigator tests for retention. In computing his ANOVA table, he sees that his MS within groups is larger than his MS between groups. What does this result indicate?
A
An error in the calculations was made
B
There was more than the expected amount of variability between groups
C
There should have been additional controls in the experiment
D
There was more variability between subjects within the same group than there was between groups
