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# Question about Confidence Interval & Sample size

1. A promotion campaign is being planned to encourage people to reduce heat in their homes. In order to measure the campaigns impact, we want to determine the proportion of people who reduce their heat at night. A telephone sample will be taken before and after the campaign.
A. What sample size is required if an accuracy of +/-0.03 is desired at a 90 percent confidence level?
B. At a 95 percent confidence level?
C. How would you answer to part (b) change if you knew that the proportion would not exceed 0.3? What if it would not exceed 0.1?
D. Assume that a "before" measure was taken with a sample size of 400 and the sample proportion was 0.3. Generate a 90 percent confidence level estimate for the population.
2. If the proportion of people who intend to vote democratic were to be estimated at a 95 percent confidence level, what sample size should be taken.
A. If the accuracy is to be +/- 0.01?
B. If the accuracy is to be +/- 0.03?
C. If the accuracy is to be +/- 0.06?
D. Repeat the above for a 90 percent confidence.
A. If the accuracy is to be +/- 0.01?
B. If the accuracy is to be +/- 0.03?
C. If the accuracy is to be +/- 0.06?

See attached file.

There are three problems attached in one document.

#### Solution Summary

The solution provides step by step method for the calculation of confidence interval and sample size. Formula for the calculation and Interpretations of the results are also included. Interactive excel sheet is included. The user can edit the inputs and obtain the complete results for a new set of data.

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