A psychopharmacologist (a psycholgist interested in the effects of drugs and physiology) is interested in determining the effects of caffeine (from coffee) on exam performance. Twenty students from a large introductory psychology class volunteered to participate in the study; all were dedicated coffee drinkers and all drank caffeinated coffee. The volunteers were then randomly divided into two groups such that there were ten students in each group. One group of 10 students was asked to study the exam material while drinking their normal doses of coffee, and to take the exam while drinking their normal doses of coffee before the test. This group is called the "Coffee with Test" group.

The second group of 10 students was asked to study the exam material while drinking their normal doses of coffee, but to take the exam without having consumed coffee for at the least 3 hours beforehand. This group is called the "No-Coffee with Test" group. One student from the "No-Coffee with Test" group became ill and was unable to sit for the exam. The researcher recorded the number of correct responses on the exam. One could get up to 15 items correct on the exam. The scores are below.

Coffee with Test No-Coffee with Test

(Number Correct) (Number Correct)

Group 1 Group 2

8 7

10 12

14 9

12 9

9 5

9 6

13 14

8 6

12 7

11

Complete step 3 of the hypothesis testing procedure and calculate the appropriate z , t, or r. Round to the nearest hundredths place. If your calculated z , t, or r is not identical to one of the values below, but within plus or minus 0.16 of an answer below, assume it's a rounding error and select the answer that is closest to your calculated value. Ignore the minus sign if your calculated z or t is negative, but if you calculate r and it's negative, of course, write the minus sign.

Group of answer choices

.38

1.53

1.92

2.55

2.70