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Proportions (p statistics): One sample

The One sample item on the Proportions (P statistics) submenu on the Stat menu provides confidence intervals and/or hypothesis tests for population proportions in the one sample situation. The procedure is a Z test using the normal approximation to the binomial. The results are displayed in the Results panel.

To use the procedure, select the item and a dialog will pop up. The dialog will prompt the user to enter the number of "successes" and the total number of observations in the sample.

For example, suppose a poll is taken of 200 registered voters about a particular issue and it is desired to know whether the majority of all registered voters support the issue. If 112 in the sample support the issue, the data would be entered into the first dialog.

Clicking the Next -> button will allow the user to select either a confidence interval (specifying confidence level) or a hypothesis test (specifying null value of p and alternative hypothesis). To test whether a majority of voters support the issue, the null would be p=0.5 (the default) and the alternative would be "greater than".

Click on the Calculate button and the output is displayed in the Results panel. In the hypothesis testing situation, the results consist of the null value for the proportion ("p0"), the estimated proportion, the sample size ("n"), the standard error of the estimate, the Z statistic value, and its associated p value. In the confidence interval situation, the output lists the estimated proportion, the sample size ("n"), the standard error of the estimate, and the upper and lower confidence limits.