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Interval Estimation
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Proportions Interval estimation (margin of error) involves using sample data to determine a range (interval) that, at an established level of confidence, will contain the population proportion. Steps Use the z-distribution table to find the critical value for a 2-tailed test given the selected confidence level (alpha) Estimate the sampling error
where p = sample proportion q=1-p Estimate the confidence interval CV = critical value CI = p ± (CV)(Sp) Interpret Based on alpha .05, you are 95% confident that the proportion in the population from which the sample was obtained is between __ and __. Note: Given the sample data and level of error, the confidence interval provides an estimated range of proportions that is most likely to contain the population proportion. The term "most likely" is measured by alpha (i.e., in most cases there is a 5% chance --alpha .05-- that the confidence interval does not contain the true population proportion). |
