Identify the Potential Threats to Validity for the Following Studies

Essay

Identify the potential threats to validity for the following studies:
a. Dr. Grueloff gives her patients a depression inventory shortly after they begin therapy. Then, she gives them caffeine therapy for three months and gives them the inventory again. They score less depressed than when they entered therapy so she concludes that caffeine therapy works.
b. Dr. Hardloff matches two groups of patients on initial level of depression and income level. Then, he gives one group caffeine therapy and the other group regular therapy. Three months later, he retests each group and finds that the caffeine group is less depressed. Therefore, he concludes that caffeine therapy is better than regular therapy.