Wave a Magic Wand Over Your DOE Analyses

Michelle Shemo 06 April, 2015

As a member of Minitab's Technical Support team, I get the opportunity to work with many people using DOE (Design of Experiments).

People often will call after they've already chosen their design, run the experiment, and identified the important factors in their process. But now what? They have to find the best settings, but with several factors and responses, what should they do?

"I wish I had a magic wand," they sometimes say. If you do too, you’ve come to the right place.

I will show you how to use the Response Optimizer to let Minitab Statistical Software work its magic to find the best settings for your response(s). 

Suppose your factors are Time, Temp, and Catalyst. Your responses are Yield (you want to maximize it) and Cost (which you want to minimize).

Let's also suppose you've used Stat > DOE > Factorial > Analyze Factorial Design to determine the significant factors and verify the assumptions of the models. 

You must analyze your design(s) before Response Optimizer will be available because it is based on the statistical model(s) created in the analysis. If you want to view the current design for a response, just rest the mouse on the check mark in the header of the worksheet:

Your final models are:

Yield = 39.48 - 0.1026 Time + 0.01502 Temp + 0.001150 Time*Temp

Cost = 15.96 + 0.0818 Time + 0.07917 Temp - 1.159 Catalyst - 0.000128 Time*Temp + 0.01913 Time*Catalyst + 0.01389 Temp*Catalyst

Now what?

All you have to do is simply choose Stat > DOE > Factorial > Response Optimizer and specify the goal for each response:

Optimizing a Response

Click OK in the Response Optimizer dialog box, and POOF!

Just like magic, Minitab identifies the combination of input variable settings that jointly optimize both responses. (The factor settings in red produced the response values in blue.)

Optimization Plot for Designed Experiment

That’s it!  Set Time at 50, Temperature at 200, and Cost is minimized (32.076) and Yield is maximized (48.852).

Click Predict in the upper left corner to see confidence and prediction intervals for the fit(s) in the Session window:

Prediction for Cost, Yield

And there's more! Want to predict for other factor levels? No problem!  There's no need to “plug into” the equations and calculate the fitted values. Just use one or both of these methods on the Response Optimizer graph:

  1. Drag the red lines. Yes, they are interactive!
  2. Click on a red value and type a in a different value.

While working with the Response Optimizer graph, you also could save settings, show a list of settings you’ve saved, and go back to the original settings Minitab found to be optimal using the Optimizer toolbar. If you do not see the toolbar, enable it by choosing Tools > Toolbars > Response Optimizer. Rest your mouse on each button to see a description of each tool.

You can take advantage of the Response Optimizer’s magic whenever you're analyzing Factorial, Response Surface, and Mixture designs.