A study sought to determine if the ancient Chinese art of acupuncture could help infertile women become pregnant. A total of 160 healthy women undergoing assisted reproductive therapy were recruited for the study. Half of the subjects were randomly assigned to receive acupuncture treatment 25 minutes before embryo transfer and again 25 minutes after the transfer. The remaining 80 subjects were instructed to lie still for 25 minutes after the embryo transfer. Results: In the acupuncture group, 34 women became pregnant. In the control group, 21 women became pregnant.

a. Why did researchers randomly assign the subjects to the two treatments?

b. The difference in the percent of women who became pregnant in the two groups is statistically significant. Explain what this means to someone who knows little statistics.

c. Explain why the design of the study prevents us from concluding that acupuncture caused the difference in pregnancy rates.