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# Confidence interval and sample size on polls data

74. 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 1500. The allowance for error is intended to cover both sampling variability and the effect of small biases.

a. 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?

b. Would the ± term be much different if 40% of the likely voters in the sample favored the candidate?

c. Why is the quoted ± .03 larger than the ± term you calculated in part (a)?

#### Solution Preview

Allowance for error and effect of bias
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 1500. The allowance for error is intended to cover both sampling ...

#### Solution Summary

Confidence interval and sample size on polls data. Calculate the margin of error. Comparing two margin of errors

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