Many newspapers, when reporting results of political polls, say that “with 95% confidence, the results are in error by no more than +/- 3 percentage points.” The typical sample size is about 1,500. This allowance for error is intended to cover both sampling variability and the effect of small biases.
- Assume that the poll (sample) indicates that just about 50% of likely voters favor a particular candidate. How large a +/- term is required for a 95% confidence interval for the population proportion?
- Would the +/- term be much different if 40% of likely voters in the sample favored the candidate?
- Why is the quoted +/- 0.03 larger than the +/- term you calculated in Question 1?