A social psychologist wants to determine the effect of believing a task is easy or difficult on task performance. 20 volunteers were given the same puzzles to be solved. Two groups of 10 people each were formed through random assignment. One group was told that the task was difficult, and the other group was told that it was easy. Mean and population variance estimates for the number of puzzles solved is shown below:

"Difficult" "Easy" group group M (mean) 15 $2 (population 72 18 variance estimate)Figure 1 Figure 2 un w Dependent variable Dependent variable W Group 1 Group 1 N N Group 2 Group 2 O A B A B Type Type Figure 3 Figure 4 Dependent variable w Dependent variable W Group 1 Group 1 N N Group 2 Group 2 O O A B A B Type Type