One feature about the data that does differ from prior statistics is that we will have two values from each subject in our sample. So, we will need both an X distribution and Y distribution to express two values we measure from the same unit in the population. For example, if I want to examine the relationship between amount of time spent studying for an exam (X) in hours and the score that person makes on an exam (Y) we might have: X Y 2 65 3 70 3 75 4 70 5 85 6 85 7 90