Vol. 22, No. 5 - September/October 2022
Dear Experimenter,

I am happy to share another answer or two from our statistical consulting team to frequently asked questions (FAQs) about design of experiments (DOE), as well as timely alerts for events, publications, and software updates. Check it out! Feel free to get back to me via [email protected] with further questions or comments: I would really appreciate hearing from you!

Please do not send me requests to subscribe or unsubscribe, follow the instructions at the end of this message.

Sincerely,
Mark J. Anderson, PE, CQE
Engineering Consultant, Stat-Ease, Inc.

PS Quote for the day:

The elephant and the flea principle applied to selecting factorial effects.
(Page down to the end of this e-zine to enjoy the actual quote.)
BLOGS
StatsMadeEasy Blog
My wry look at all things statistical and/or scientific with an engineering perspective.
Also, see the Stat-Ease blog for tips on making DOE easy. For example, a recent posting provides insights on “Randomization Done Right." Take a look!
FAQ
How to select factorial effects from the half-normal plot

Original question from a R&D Laboratory Manager:
“Being a newly licensed user of your software and unfamiliar with the half-normal plot, I need some guidance on which effects to select from my two-level factorial experiment. At first, I figured that the main effect factor D should be chosen. This produced an impressive Pareto chart with D towering above the Bonferroni limit. However, then I saw that CE, AE, A and BC go above the line. Should I pick these effects also? (BTW, the line appears a bit choppy because I blanked out the names of the factors to keep them confidential.)”

An over-selection of effects by a new user

Answer:
Pay no attention to effects being above the line—only ones off to the right. As you first suspected, only the main effect of D should be chosen in your case—all the other effects falling in line. After you deselect all effects except for D, you will notice a large gap beyond the largest of the “trivial many” effects (CE). This is characteristic of a good selection of effects from the half-normal plot.

In the future, be on guard for over-selection of effects. By the “sparsity of effects’ principle, expect to see emergent (falling to the right on the half-normal) only about 20% of main effects and two-factor interactions (higher order than this being very rare). Always select the largest effect first and any others that fall off to the right of those lined up nearer zero. For example, see this video. For a more detailed briefing on the half-normal plot and other graphical selection tools presented by me this past July, visit this webinar.


PS to DOE FAQ Alert readers: Refer to this issue’s quote about the “elephant and flea” that warns against over-selection of factorial effects.

(Learn more about selecting factorial effects by enrolling in the workshop Modern DOE for Process Optimization.)
EVENT ALERT

(FINAL NOTICE) We invite you to join us for the Stat-Ease 2022 Online DOE Summit on October 4-6—the world’s premier conference on practical applications for design of experiments. Our Summit is presented virtually, free of charge! The agenda is shaping up with fun and informative talks, such as:
  • “The Magic of Multifactor Testing” (my contribution!),
  • “Case Cracked: Setting Process Windows with Design-Expert” and
  • “Saving the Mega Blaster from Disaster”.
These are just a few of the planned presentations that cover a wide range of topics and industries. Get ready for many entertaining and educational talks on making the most from industrial experiments.

See the entire lineup and register now at our DOE Summit site.


PS Attend the Day 2 presentation on "The Latest and Greatest in Design-Expert and Stat-Ease 360" to be entered into a drawing for a free copy of DOE Simplified: Practical Tools for Effective Experimentation, 3rd Edition (US and Canada attendees only).
WORKSHOP ALERT
Sharpen up on DOE—Enroll before classes fill

You can do no better for quickly advancing your DOE skills than attending a Stat-Ease workshop. Our expert instructors provide you with a lively and extremely informative series of lectures interspersed by valuable hands-on exercises. Enroll early to ensure your spot! See this web page for the complete schedule of upcoming Stat-Ease courses. To enroll in the workshop that suits you best, click Register on that webpage, or click here to contact us.
 
PS If you lead a group of 6 or more colleagues, save money and customize content via a private workshop. For a quote, please contact us
“Per the 'Elephant and the Flea Principle' (when you want to weigh the elephant, don't worry about [its] fleas), if you think main effects and low order interactions are big and high order interactions are small, then don't sweat the high order interactions.”
 

—University of Minnesota Professor Gary Oehlert, author of A First Course in Design and Analysis of Experiments.
Stat-Ease, Design-Expert and Statistics Made Easy are registered trademarks of Stat-Ease, Inc.

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