Exercise 7.11.5

Model Answers to 07 Hypothesis Testing in Six Sigma Statistics using Minitab 17, Green Belt Edition.

Example 7.11.5

Conduct a 2 sample StDev Test


Analyse the data in File 07Hypothesis Testing.xlsx worksheet Ex 7.11.5 and answer the questions shown below. The data was collected randomly and is recorded in time order.

  1. Is the sample data in columns TempA and TempB likely to have come from populations with differing means?
  2. If the populations are different, which population mean is greater?
  3. Have the requirements of the test that you have used been met?
  4. What was the Power of the test when you want to detect a difference of 5?
  5. Are there any issues associated with this level of  Power ?
  6. Does the Report Card generate any warnings?





Set-Up

Analysis

1.  Click Stat<<Assistant<< Hypothesis Test

2. Click on 2 Sample StDev Test




2.  Complete the menu as shown and click OK to execute the procedure.


Starting at the top left of the Summary Report we can conclude that the sample data within columns TempA and TempB is likely to have come from different populations.





From the histograms under the Distribution of Data we can see that the 95% CI for the mean of TempB is greater than TempA



On the Diagnostic Report we see that the control chart for TempB in the diagnostic report shows that there has been a shift of mean value at some point within the data collection process. The shift in mean is probably due to an external factor that we have not recognised.

This means that the conclusions from our test results are likely to be wrong. We need to identify the unknown factor and control it’s influence on the results. We can then redo the data collection and analysis.

There is no value looking at the Power level.






The Report Card does not show any warnings