1. What are the differences between an observational study and an experiment?

2. explain the following four principles of experimental design.

(a) Control:

(b) Randomize:

(c) Replicate:

(d) Block:

3. What does the term "statistically significant" mean?

4. What is the difference between a "control treatment" and a "control group?"

5. What is "blinding?"

6. What is the difference between a "single-blind" experiment and a "double-blind" experiment?

7. What is a placebo?

8. What is blocking?

9. What does the term "confounding" mean in statistics?

10. Describe the similarities and differences in "confounding variables" and "lurking variables."

11. Recently a group of adults who swim regularly for exercise were evaluated for depression. It turned out that these swimmers were less likely to be depressed than the general population. The researchers said that the difference was statistically significant.

a. What does "statistically significant" mean in this context?

b. Is this an experiment or an observational study?Explain.

c. News reports claimed this study proved that swimming can prevent depression. Explain why this conclusion is not justified by the study. Include an example of a possible lurking variable.