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Stat > Basic Statistics > 2 Proportions

Performs a test of two binomial proportions.

Use the 2 Proportions command to compute a confidence interval and perform a hypothesis test of the difference between two proportions. Minitab offers two hypothesis tests for the difference between two proportions: Fisher's exact test, and a test based on a normal approximation. The normal approximation test may be inaccurate for samples in which the number of events in either sample is less than five, or if the difference between the numbers of trials and events in either sample is less than five. Fisher's exact test is accurate for all sample sizes, but can only be calculated when the null hypothesis states that the population proportions are equal. In other words, Minitab only performs Fisher's exact test when you specify a test difference of zero in the Options subdialog box.

For example, suppose you wanted to know whether the proportion of consumers who return a survey could be increased by providing an incentive such as a product sample. You might include the product sample with half of your mailings and see if you have more responses from the group that received the sample than from those who did not. For a two-tailed test of two proportions:

H0: p1 - p2 = p0 versus H1: p1 - p2 ≠ p0

where p1 and p2 are the proportions of events in populations 1 and 2, respectively, and p0 is the hypothesized difference between the two proportions.

To test one proportion, use Stat > Basic Statistics > 1 Proportion.

Both samples are in one column: Choose if you have entered raw data into a single column with a second column of subscripts identifying the sample.

Samples: Enter the column containing the raw data.

Sample IDs: Enter the column containing the sample subscripts.

Each sample is in its own column: Choose if you have entered raw data into single columns for each sample.

Sample 1: Enter the column containing the raw data for the first sample.

Sample 2: Enter the column containing the raw data for the second sample.

Summarized data: Choose if you have summary values for the numbers of trials and events.

Sample 1

Number of events: Enter the number of events in the first sample.

Number of trials: Enter the number of trials in the first sample.

Sample 2

Number of events: Enter the number of events in the second sample.

Number of trials: Enter the number of trials in the second sample.