Suppose that you want to compare proportions of registered Democrats, Independents, and Republicans who have donated blood within the past year.
a. Which would be appropriate for this study: random sampling, random assignment, both, or neither? Explain.
b. If you find that the sample proportions who have donated blood are 0.20, 0.15, and 0.12, what more information would you need to determine if these proportions differ significantly?