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# Confidence Interval, Sample size and Margin of error

() is a pi symbol.

2. In the next presidential election of year 2012, five candidates running for the election are Sarah Palin, Hilary Clinton, Barack Obama, Mitt Romney, and Rudy Giuliani. It is desired to estimate the true proportion ( ) favoring one of the five candidates.
a) based on sample size 1000 with 92% confidence, how close (plus or minus) should we expect our estimate to be to the true value of the proportion ( )?
b) If we wanted to be 99% sure that our estimate was within 0.05 of the true value, how large the sample size should be?
c) If 470 in the sample of 1000 were found to prefer Sarah Palin, what is the lower limit of the two-sided 90% confidence interval for the true proportion ( )?

#### Solution Summary

The solution provides step by step method for the calculation of confidence interval for population proportion, sample size and margin of error. 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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