DESCRIPTIVE STATISTICS EXERCISE

Instructions: Below are data from a fictional two-factor experiment. Compute mean and standard deviation for each condition according to the instructions given. In addition, compute the marginal means for both factors.

Dr. Readalot conducted a study examining the effectiveness of different kinds of studying. He had students study either for 5 hours the night before the test (crammed study) or for 1 hour each of the five nights prior to the test (distributed study). Additionally, he was interested in whether the kind of material being studied (and tested) would interact with the method of studying (math or vocabulary). He tested five participants in each of the four conditions. The test score (in percentage correct) for each participant is presented in the table below. Follow the instructions given below the table.

Marginal Means for Type of Material

1. Compute the Crammed Math condition mean. Record your answer into the table on the previous page.

Step 1: Add up the five scores.

Step 2: Divide the total by 5 (the number of scores).

2. Do the same for the other three conditions. Record your answers into the table.

3. Compute the Crammed Math condition standard deviation. Record your answer into the table.

4. Do the same for the other three conditions. Record your answers into the table.

5. Compute the marginal means for study method. Record your answers into the table.

Add up all of the scores in the crammed condition (that's 10 scores, 5 from math and 5 from vocabulary). Then divide by 10 (the total number of scores in the crammed condition). Repeat the process for distributed studying.

(Hint: Don't just add the two means together and divide by 2. This will work for this example, but only because there are equal numbers of scores in the two conditions. If there are unequal numbers in your conditions, you will get the wrong number.)

6. Repeat the process to compute the marginal means for the material type. Record your answers into the table.