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The Complete Idiot's Guide to Statistics, 2nd Edition by Robert Donnelly

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Confidence Intervals for the Proportion with Large Samples

We can also estimate the proportion of a population by constructing a confidence interval from a sample. As you might recall from Chapter 13, proportion data follow the binomial distribution that can be approximated by the normal distribution under the following conditions:
np ≥ 5 and nq ≥ 5
where:
p = the probability of a success in the population
q = the probability of a failure in the population (q = 1 - p)
Suppose I want to estimate the proportion of home shopping customers who are female based on the results of a sample. In Chapter 13, we learned that we can calculate the proportion of a sample using:

Calculating the Confidence Interval for the Proportion

The confidence ...

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