When a person experiences ____________, it becomes difficult for a normal circadian rhythm to be maintained, which can lead to signs of depression and anxiety.

Suppose a researcher is performing an experiment on children. She tests the children on one level of the independent variable at the beginning of the school year, but cannot return to test the second level until mid-April, when the school year is almost completed. What threat to internal validity may be a problem?

a. History b. Selection bias c. Maturation d. Experimenter bias

How long can Bart, an American, expect to live in good health, free of disabilities?

A. 61 years B. 88 years C. 78 years D. 53 years