Researchers reported that unmarried men are more likely to suffer from clinical depression than married men. These findings were based on the marriage histories of 700 men suffering from depression and 600 men not suffering from depression. Determine the nature and scope of the conclusion the study can reach.

a. For American men, getting married will result in a decreased risk of depression.
b. Since there is no random assignment, there is no way to know that being unmarried increases the risk of depression; there may have been confounding variables.
c. Since there is no random assignment, there is no way to know that being unmarried increases the risk of depression; there may have been lurking variables.
d. For men, getting married will result in a decreased risk of depression.
e. Since the study involved only men, there is no way to know that being unmarried increases the risk of depression.