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# Two Sample Poisson Rate Help

The two sample Poisson rate technique is used to determine if two rates of occurrence differ for two processes or groups.   A confidence interval can be calculated to define a range of values that are likely to contain the difference in the two rate.  This interval can be one or two sided.

The example below demonstrates how to do this test.  You can download the data at this link.

The owner of two restaurants wants to know if the number of customers per day per restaurant is the same or not.  He collects data for 30 days.   The steps to perform the two sample Poisson Rate analysis are given below.

1. Enter the data into a worksheet as shown below. The data must be in two columns, one for each group.

2. Select the data above (including the heading).

3. Select “Poisson Rate Tests” from the “Statistical Tools” panel in the SPC for Excel ribbon.

4. Select the “Two Sample Poisson Rate.” The input form below is shown.

#### Two Sample Poisson Rate Output

The output from the two sample Poisson rate technique is shown below.  In this example, the hypothesized rate difference is 0.  It is a two-side hypothesis test with alpha = 0.05.

An explanation of terms is given below the output.  In addition to the output table, the program displays charts to help interpret the results.

The output tells you the conclusion from the test.  The null hypothesis (H0) and the alternate hypothesis (H1) are printed below the title.

The chart below is also created.  This makes it easy to see if the hypothesized rate is within the confidence interval or how far away it is from the confidence interval.

There is also a chart for each data set to look for possible outliers.  If the program detects possible outliers, they will be in red and a message will be printed on the worksheet.

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