A retrospective study of 517 veterans who never smoked was done to determine whether there was an association between lung disease and exposure to workplace gases, dust, and fumes (Clawson, Stanford Report, November 1, 2000).

In given study, subjects were asked whether or not they remembered being exposed to gases, dust, or fumes in the workplace. A concern expressed by the investigator was that "patients who have histories of lung diseases may be more likely to recall a history of exposure-whether accurate or not-than subjects reporting good health." Discuss whether each of the following is likely to be a problem in this study.

a. Relying on memory.

b. Confounding variable.

c. Hawthorne effect.