Class: Psychology - Introduction to Statistics

Part I: Computing Pearson r values by Hand

A researcher asks 7 students to report how many caffeine-based energy drinks they consume each day for a week and the number of hours they sleep each night for that week. The researcher then computes the average number of drinks each student consumes per day and the average number of hours they sleep per day. The data are below.

Energy Drinks/Day	Hours slept/Day
5	3
3	5
0	5
1	5
7	2
1	8
1	6

Questions: Compute (AND SHOW WORK) the Pearson Product Moment Correlation Coefficient (r) using the z-score formula.

1. On your paper create 5 columns labeled, x, y, zx, zy, and zxzy
2. Start by putting in the values of x and y in their respective columns
3. Calculate the mean and SD for x (put these at the bottom of the x column) Compute the population SD: the one with N in the denominator
4. Calculate the mean and SD for y (put these at the bottom of the x column) Compute the population SD: the one with N in the denominator
5. Calculate the z scores for x (put them in the right column)
6. Calculate the z scores for y (put them in the right column)
7. Calculate the cross products of the z scores for x and y (multiply every zx by every zy)
8. Divide the sum of the zxzy column by N to get r: label your answer somewhere obvious on your paper.