If the size is less than 30, the small sample case is selected.Small or Large Sample Case: this determines the case to use for the calculations the default is based on the sample size.If you select this option, you must include a hypothesized difference.

Include Hypothesis Test: this option will include a hypothesis test in addition to the confidence interval.Process 2 Data with Headings: enter the range containing process 2 data along with the headings default is the column next to process 1 data.Process 1 Data with Headings: enter the range containing process 1 data along with the headings default is the range selected on the worksheet.Select OK and the input form below is displayed. Select the 'z and t Tests for Difference in Two Means' option from the 'Sample Tests' form. Select 'Sample Tests' from the 'Statistical Tools' panel in the SPC for Excel ribbon.Ĥ. Select the data shown above including the headings.ģ. The data can be downloaded at this link.Ģ. Enter the data into a worksheet as shown below. We want to see if there is a difference in the means from the two processes.ġ. The question is whether each process places the same weight into the bags. The example below demonstrates how to do this test using data in a range in the worksheet.Ī company uses two different processes to put sand into bags. The data can be in a range in a worksheet or the user can enter an average, standard deviation, and sample size for the two processes. You also have the option for a two-sided, lower one-sided or an upper one-sided test. z test: This test uses the z distribution and is usually used with larger sample sizes (> 30).t test: This test uses the t distribution and is usually used with smaller sample sizes although it can be used with any sample size.The test accounts automatically for variances that are equal or unequal. The test will provide a confidence interval for the difference in two means and has the option for hypothesis testing as well. This test compares the means of two samples.

Confidence interval for sample means