Answer:
The dependent variable measured in the researcher’s experiment is the concentration of the drug in the blood samples. One control that the researcher could use to improve the validity of the experiment is to ensure that the same amount of the drug is administered to each participant.
Analyzing blood samples at many intermediate time points instead of at only the beginning and the end of the 20-week period allows the researcher to track changes in the concentration of the drug over time. This gives a more accurate picture of how the drug is metabolized by the body and how it affects the participants.
Step-by-step explanation: