Which of the Following Examples Involves Paired Data

Multiple Choice

Which of the following examples involves paired data?

A) A psychologist compares two methods of memorizing information. Twenty people use one method and twenty other people use the second method.
B) A researcher estimates the difference between the mean forearm lengths of men and women based on a random sample of each.
C) A medical researcher measures the cholesterol levels of each of 30 heart attack patients 2 days after the attack and again 4 days after the attack.
D) A marketing research expert estimates the proportion of the 22 to 29 year-old age group that says they might buy a new car in the next two years