Vol. 21, No. 3 - May/June 2021
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 mark@statease.com 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.

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

PS Quote for the day:

Sage advice from the late famed chef Anthony Bourdain.

(Page down to the end of this e-zine to enjoy the actual quote.)
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 tips for “Avoiding Over-Selection of Effects on the Half-Normal Plot”. Take a look!
Software Alert
Version 13.0.5 of Design-Expert software released

Current Design-Expert v13 (DX13) users will do well by updating to 13.0.5 via Help from within your installed program. View the changelog for details on the changes—mainly maintenance items. If you want to receive notice when an update becomes available, go to Edit on the main menu of your program, select Preferences and, within the General tab (gear icon), turn on (if not already on by default) the “Check for updates” option. (This alert feature is not available in network versions.)

If you remain mired in an obsolete version or are not yet a user of Design-Expert, click here for the highlights on what’s new in DX13 plus more details on added features via this link. Then, assuming you like what you see, follow the FREE TRIAL link for a 14-day tryout, or buy it directly taking advantage of upgrade pricing if eligible.
Advisability of minimal-run small central-composite design for optimizing a process

Original question from a College of Pharmacy Professor:
“Thank you for your very informative DOE FAQ Alerts. I am a research scholar in pharmaceutical sciences using Design-Expert software for my design and analysis of experiments. I have tried different response surface designs offered by your program. To save time, I am now considering a 15-run small central-composite design (SCD) for a three-factor optimization experiment. What are your thoughts on ‘cutting corners’ via SCDs?”

As Design-Expert (DX) software warns upon selection of SCDs, these near minimal-run templates do not withstand outliers nearly as well as the far stouter conventional CCDs. In your case for three factors, the extra 5 runs for the full 20-run CCD will be a solid investment in reduced leverages and variance inflation factors (VIFs). See this for yourself by doing design evaluations with the outstanding tools provided by DX.

As I once heard George Box, the co-inventor of CCDs, say: “When in doubt, build it stout.” As you know being an experienced DOE practitioner, runs often go awry due to so many factor changes and response measurements. Therefore, we advise using SCDs only as a last resort.

By the way, for 6 or more factors, Design-Expert offers CCDs with minimum-run resolution V cores. This unique response-surface design option reduces the number of design points substantially without putting the experimenter in jeopardy of outliers. Nice!

- Mark
(Learn more about response surface methods (RSM) by attending the next distance-learning presentation of Modern DOE for Process Optimization.)
Free Webinars - Sign up Now to Take Advantage:
Check out these highly educational presentations coming soon from our world-class DOE experts:
  • June 28—“Deploying DOE to Predict Process Performance” by Shari Kraber
  • July 21—“DOE for Ruggedness Testing” by me
  • July 28—“New-User Intro to Design-Expert Software” by Richard Williams
Click here to view the times, descriptions and registration links for these upcoming live webinars. Sign up now to advance your DOE know-how!
Sharpen up on DOE—Enroll before summer 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
“Without experimentation, a willingness to ask questions and try new things, we shall surely become static, repetitive, and moribund.”
—Anthony Bourdain
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