Using the Time Series Plot in Minitab to Show Changes in the Y (or Output)
The only way you can quantify the effect on the process that you are trying to improve is by using quantitative data (metrics). If you are not using metrics to prove effect, then you are using your opinion.
I tell my students “No one cares about your opinion”. That may sound crass, but opinions, judgements, “shooting from the hip” can all be incorrect. This can leave you open to a lot of questions by your stakeholders.
Quantitative Data (Metrics) that have been proven reliable with an MSA are relatively bullet proof.
In my experience, the best tool for Tracking changes in the Y is the Time Series Plot.
As you make changes to the process during any of the DMAIC stages, there should be a measurable effect. The Time Series chart will plot the effect.
Hint, be sure to use a time scale on your time series plot to show the dates of each improvement (see picture below)
The Time Series Plot is a simple tool for your Stakeholders to show progression of the project over time.
Let’s learn how to create the time series plot in the picture above using Minitab 17
First, we need the data:
Next, we will open the Time Series Plot:
In the Minitab Menu Bar, go to “Graph” and then click on “Time Series Plot”
In the Time Series Plots dialogue box (see picture below) choose “With Groups”. We do this because we are tracking within the DMAIC Stages.
Next, We fill in the “Time Series Plot With Groups” dialogue box as shown in the picture below.
We then click on the “Time/Scale…” button to add the Time Scale that we have defined in our data in the column “Date”
The “Time Series Plot: Time/Scale” Dialogue box will open. Click on “Stamp” and choose the “Date” column.
Now click on the “Reference lines” tab. Enter “35” under “Show reference lines at Y values:”. This is the target for your Y value that should be referenced in your “Goal (or Objective) Statement” in your Project Charter.
Click on “OK” and then click on “OK” again and you should produce the following Time Series Plot: