Which of these are threats to validity in the following

Last updated: 2/8/2023

Which of these are threats to validity in the following study Dr Knudsen a family physician wanted to test the effect of a new drug on depression So she prescribed a daily dose of the drug to each of her 23 depressed patients for a period of three weeks and measured their level of depression before and after they began treatment Since her patients report less depression at the end of three weeks she concluded that the new drug reduces depression Wrong study design to test causation Experimenter bias Sample Bias All of the above