Please help with these questions!

1. For a study of factors associated with iron nutrient absorption, a researcher uses a radiopharmaceutical to observe and measure this process in a sample of 200 patients. Would you characterize the resulting data as observational or experimental? Explain.

2. A researcher is interested in the potential for using acupuncture to improve post-operative recovery of individuals who have had hip replacements. They collect data on 50 patients who have undergone this surgery and been given acupuncture therapy. (a) Do they have observational or experimental data? (b) What is the implicit population for which these 50 cases are a sample?

3. Suppose you are doing a study of long Covid; you have a random sample of Portland residents who have tested positive for the disease, and you gather data on them at one, three, and six months post-infection. Unfortunately, a significant number of them move during the study period, removing them from the sample. How might you check to see in what ways and to what extent the unbiasedness of your sample has been compromised?