Assume you want to determine the proportion of people in your community who would select Thin Mints as their favorite Girl Scout cookie. Also assume previous studies have shown this proportion to be around .4 .
a. Find out how many people you would have to sample in order to determine this proportion to in .025 with 95% confidence.
If your boss says that this number (your answer to part a) is too large to be practical, you may respond that the smaller sample size would suffice if either the margin-of-error (.025) or confidence level (95%) were changed.
b. In which direction would the margin-of-error need to change in order for a smaller sample size to suffice?
c. In which direction would the confidence level need to change in order for a smaller sample size to suffice?