(Illustration) Confirmation of the improvements

Confirmation of the improvements

Linda : The measurement system validation in step 1 gave us final confirmation of the tolerance range established by the D O E. Now, the goal in step 2 is to statistically confirm that the improvements have positively impacted the nut removal process.

Linda : Confirmation in Six Sigma means statistics that will back up your decisions. I know not everyone loves stats, but the good news is, in step 2, we are using calculations that you have already learned!
Linda : When you get finished with this step you will be able to apply the process capability and hypothesis testing that you learned in Analyze to the Control phase.

Linda : You may be thinking that it's been a while since Analyze and it's not entirely clear why these tests are repeated during Control.
Linda : All previous steps have led us to believe that the nut removal process at Rockledge will be improved by using New Torque Master Nuts and by setting the torque level on the wrench to 17,000 foot pounds during installation.
Linda : But remember that reaching Six Sigma requires in-depth statistical analysis. Based on the six sigma process, you believe that those improvements will have a beneficial impact on your project Y of reducing nut installation time, but have you statistically confirmed that it does?
Linda : Process capability is the measure for how a process is performing, so to verify that our process is doing better, we need to re-calculate that number now.
Linda : You'll actually recalculate during the pilot phase to see if the capability has improved, then calculate it again after the improvement has gone live in the workplace. The second "real-world" calculation should only happen after enough time has passed to allow sufficient sampling and the process is believed to be in control. For the purpose of this training, that means after you have completed the control tasks presented in Step three.
Linda : A second type of improvement evidence is the result from a hypothesis test. In the Rockledge case that will mean hypothesizing that there has been a change in the nut removal process versus no change in the process.
Linda : Since this means comparing the mean of the original data collected on the nut removal process with data collected after the improvement, and this is continuous data, a two-sample T test is the best choice of analysis.
Linda : Now that you understand why we are performing these analyses, let's get to it!.

Linda : Since we haven't decided on our control strategies in the workplace yet, we are going to be evaluating the capability of the pilot process.
Linda : As always, we've got to begin with the data. This data set was collected over the course of three scheduled outages at the pilot site. The time was measured for removing twenty-two randomly selected bolts on a different gas turbine during each outage.
Linda : Generating the process capability report for this data in Minitab -- as you learned to do in the Analyze phase -- we get the following summary of the Sigma values.
Linda : And, comparing those numbers to the original Z-bench scores for this nut removal process, has the process improved?
Linda : There is an over four-sigma improvement in the process capability and, most importantly, the Defects per Million Opportunites has dropped from around one hundred forty thousand to zero. This is statistical confirmation that in the pilot testing environment, the improvements made to the X's have had a positive impact on the project Y. This report should be generated once again on measurements of the process in its full implementation for confirmation of the process improvement in the real world.

Linda : The final confirmation of success in the Rockledge case is the result from a hypothesis test, because it provides 95% confidence in our decision that we've made an improvement. Which answer best describes our hypothesis for this test?

Linda : To review what we covered in this lesson, you should now be able to apply what you learned in the analyze phase,
Linda : to evaluate the process capability and hypothesis test results for statistical confirmation of the process improvements.

Linda : And in the Rockledge Case, with a dramatically higher sigma score and the definitive results of a hypothesis test, we can now confirm that the process improvements made during the Improve phase, have had a positive impact on the project goal of reducing nut removal time.

Linda : Well, time flies when you are having fun -- I told you I enjoyed my work, didn't I!? We've reached the end of step 2 and you are almost at the end of Duh-may-ic.