1) A college statistics instructor wanted to investigate the relationship between age (in years) and a measure of flexibility. Flexibility was measured by asking a person to bend at the waist as far as possible, extending his or her arms toward the floor. Using a yardstick, the distance from the floor to the fingertip closest to the floor was measured (in inches). Negative measurements indicate going beyond just touching the floor.

Age and the measure of flexibility just described was measured for a group of 28 students in the instructor's class. The goal was to determine if there is a relationship between age and this measure of flexibility. What are two reasons why it would not be a good idea to use just the students in your class as the subjects for your study?