Issue: Volume 5, Number 4
Date: April 2005
From: Mark J. Anderson, Stat-Ease, Inc. (http://www.statease.com)

Dear Experimenter,

Here's another set of frequently asked questions (FAQs) about doing design of experiments (DOE), plus alerts to timely information and free software updates. If you missed previous DOE FAQ Alerts, please click on the links at the bottom of this page. If you have a question that needs answering, click the Search tab and enter the key words. This finds not only answers from previous Alerts, but also other documents posted to the Stat-Ease web site.

Feel free to forward this newsletter to your colleagues. They can subscribe by going to http://www.statease.com/doealertreg.html. If this newsletter prompts you to ask your own questions about DOE, please address them via mail to: StatHelp@StatEase.com.

Here's an appetizer to get this Alert off to a good start: http://www.globalspec.com/trebuchet/.  This web site enables you to experiment on a virtual trebuchet. For background on this war machine see http://www.statease.com/news/news0306.pdf, which details a DOE I did on a trebuchet made for educational purposes. I found it embarrassing that our first few shots backfired due to using overly heavy projectiles.  However, worse things have happened: During the 1521 siege of the Aztec's capital city by the Spanish conquistador Cortes, his engineers  got their trebuchet settings wrong and sent a boulder straight up.  It then came straight down and demolished the machine. Nevertheless, the Spanish prevailed, as seen in ruins unearthed below Mexico City: http://www.metmuseum.org/toah/hd/teno_1/hd_teno_1.htm.

Here's what I cover in the body text of this DOE FAQ Alert (topics that delve into statistical detail are designated "Expert"):

1. Newsletter Alert: The May issue of the Stat-Teaser features mixture design for the optimization of an exotic fruit nectar
2. FAQ: Are center points needed for two-level factorial design?
3. Free books (US/Canada only): Winners of the drawing for "Engineering Statistics" and "RSM Simplified" texts
4. Info Alert: An illuminating DOE on a cell phone display
5. Events alert: Talks across the USA at Spring conferences for chemical engineers, cosmetic chemists, pressure sensitive tape experts, quality professionals and coatings researchers
6. Workshop alert: See when and where to learn about DOE
7. Help wanted: Stat-Ease is seeking an enthusiastic DOE trainer

PS. Quote for the month: Cynical views of what makes a person an expert

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1. Newsletter alert: The May issue of the Stat-Teaser features mixture design for the optimization of an exotic fruit nectar

Many of you by now may have received a printed copy of the latest Stat-Teaser, but others, by choice or because you reside outside of North America, will get your first look at the May issue at http://www.statease.com/news/news0503.pdf.

The feature article, "Mixture Design Enhances the Nectar from an Exotic Amazonian Fruit," shows how a Portuguese food scientist made good use of statistical design of experiments.

The other article announces a new, one-day "crash course" on DOE for sales and marketing.  It will be presented at the Stat-Ease training center in Minneapolis by Dr. Paul Selden on September 29. See http://www.statease.com/clas_smdoe.html for information on this class, background on the instructor, a syllabus and links to sign up online.

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2. FAQ: Are center points needed for two-level factorial design?

-----Original Question-----
From: Switzerland
"I am designing a chromatography experiment.  It will be very time-consuming.  Therefore, we must reduce the number of runs to be performed to the minimum.  I set up a full, two-level factorial design.  Must I add center points to determine the variability of the response?  If not, this would save me valuable time doing the chromatography."

Answer (from Stat-Ease consultant Pat Whitcomb):

"A full two-level factorial allows estimation of a factorial model.  For two factors (A and B) the factorial model is: Ypred = ß0 + ß1A + ß2B + ß12AB.

Factorial models usually include a subset of the main effects and two-factor interactions.  (Higher order interactions can be estimated but are rarely significant.)  A model with main effects and interactions allows a twisted plane to be used to model response behavior.  Going to a full quadratic model would allow the edges of the twisted plane to be curved rather than linear.

Adding center points allows a test to see if there is significant curvature in the region being explored. Curvature estimates the significance of the aliased string of squared terms: A^2 + B^2 + etc.  If curvature is detected, then the factorial with center points must be augmented with additional runs to allow estimation of the individual squared terms.

For any given response a factorial model will find the maximum or minimum at a vertex of the design space.  If you believe the max/min is inside the cube you should use a response surface rather than a factorial design."

To reinforce Pat's comments, note that four center points add 50 percent more runs to a full two-level design on three factors.  (We advise running at least this many to provide adequate power for the curvature test).  If an experimenter believes they have neared the peak of performance, this investment would be worthwhile, otherwise not. For discussion on strategy of experimentation, see Chapter 1 of "RSM Simplified" at http://www.statease.com/pubs/rsmsimpexcerpts--chap1.pdf.

—Mark

(Learn more about center points and two-level factorial design by attending the three-day computer-intensive workshop "Experiment Design Made Easy."  See http://www.statease.com/clas_edme.html for a course description. Link from this page to the course outline and schedule.  Then, if you like, enroll online.)

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3. Free books (US/Canada only): Winners of the drawing for "Engineering Statistics" and "RSM Simplified" texts

Sorry, due to the high cost of shipping, this offer applied only to residents of the United States and Canada, 74 of whom sent me an e-mail that they'd appreciate one of four free copies of "Engineering Statistics" (Montgomery, Hubele and Runger, 2nd Ed., Wiley, 2001) and/or a newly-published "RSM Simplified" book* autographed by the authors (myself and Stat-Ease consultant Patrick Whitcomb).

The winners of "Engineering Statistics," chosen at random from my stack of requests using Design-Expert® software, are:
—James Akers, Illinois
—Angela Clark, GE Advanced Materials (USA)
—Mark Stachowiak, Hemlock Semiconductor Corporation (USA)
—Joseph Levy, New York

Our autographed "RSM Simplified" goes to:
—Fred Dombrose, North Carolina.

Thank you to all who participated in this drawing.  If it's any consolation for those who did not win, Stat-Ease will likely free up more of these textbooks, or others of like quality, in future as they are replaced with newer editions.

*(For details, including sample chapters, on this soft-cover text accompanied by version 7 of Design-Expert software for educational use, see http://www.statease.com/rsm_simplified.html.)

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4. Info alert: An illuminating DOE on a cell phone display

See how Charles Zovko, Senior R&D Engineer in the Durel Division of Rogers Corporation, used mixture design to discover an ideal pigment combination for electroluminescent cells used for cell-phone backlighting.  His original manuscript, including Design-Expert screen shots, is posted at http://www.statease.com/pubs/backlightingmixdesign.pdf.  To see the edited version published in "Product Design and Development," click http://makeashorterlink.com/?G60F35A9A.

(To learn more about the tools used by Zovko, attend our "Mixture Design for Optimal Formulations" workshop.  For a description, see http://www.statease.com/clas_mix.html.  Link from this page to the course outline and schedule.  You can enroll online by linking to the Stat-Ease e-commerce page for workshops.)

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5. Events alert: Talks across the USA at Spring conferences for chemical engineers, cosmetic chemists, pressure sensitive tape experts, quality professionals and coatings researchers

Stat-Ease statistical consultants will be all over the USA over the next few months speaking to a wide variety of industries.  For all the details and links to specific conferences, click on http://www.statease.com/events.html.  We hope to see you sometime in the near future!

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6. Workshop alert: See when and where to learn about DOE

See http://www.statease.com/clas_pub.html for schedule and site information on all Stat-Ease workshops open to the public.  To enroll, click the "register online" link on our web site or call Stat-Ease at 1.612.378.9449.  If spots remain available, bring along several colleagues and take advantage of quantity discounts in tuition, or consider bringing in an expert from Stat-Ease to teach a private class at your site.  Call us to get a quote.

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7. Help wanted: Stat-Ease is seeking an enthusiastic DOE trainer

Stat-Ease is seeking an enthusiastic trainer for our design of experiments workshops. Responsibilities may also include writing/editing technical materials and providing statistical support to clients. The ideal candidate is local to the Minneapolis area, has hands-on experience in industrial experimentation, and has teaching experience. Contract, full-time, or part-time. 30% travel. E-mail resume to Shari Kraber at Mailto:Shari@statease.com.

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I hope you learned something from this issue. Address your general questions and comments to me at: Mark@StatEase.com.

Sincerely,

Mark

Mark J. Anderson, PE, CQE
Principal, Stat-Ease, Inc. (http://www.statease.com)
2021 East Hennepin Avenue, Suite 480
Minneapolis, Minnesota 55413 USA

PS. Quote for the month—Cynical views of what makes a person an expert:

"An expert is a person who tells you a simple thing in a confused way, in such a fashion as to make you think the confusion is your fault."
—William B. Castle, Medical Scientist

(Wally) "People think I'm worthless, but in fact I'm a subject-matter expert in a very narrow field.  It's so narrow that it requires no knowledge whatsoever."
(Dilbert) "What field is it."
(Wally) "There's no way to know for sure."
—Scott Adams cartoon (http://www.dilbert.com/)

Trademarks: Design-Ease, Design-Expert and Stat-Ease are registered trademarks of Stat-Ease, Inc.

Acknowledgements to contributors:
—Students of Stat-Ease training and users of Stat-Ease software
—Fellow Stat-Ease consultants Pat Whitcomb and Shari Kraber (see http://www.statease.com/consult.html for resumes)
—Statistical advisor to Stat-Ease: Dr. Gary Oehlert (http://www.statease.com/garyoehl.html)
—Stat-Ease programmers, especially Tryg Helseth (http://www.statease.com/pgmstaff.html)
—Heidi Hansel, Stat-Ease marketing director, and all the remaining staff

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Interested in previous FAQ DOE Alert e-mail newsletters?
To view a past issue, choose it below.

#1 Mar 01
, #2 Apr 01, #3 May 01, #4 Jun 01, #5 Jul 01 , #6 Aug 01, #7 Sep 01, #8 Oct 01, #9 Nov 01, #10 Dec 01, #2-1 Jan 02, #2-2 Feb 02, #2-3 Mar 02, #2-4 Apr 02, #2-5 May 02, #2-6 Jun 02, #2-7 Jul 02, #2-8 Aug 02, #2-9 Sep 02, #2-10 Oct 02, #2-11 Nov 02, #2-12 Dec 02, #3-1 Jan 03, #3-2 Feb 03, #3-3 Mar 03, #3-4 Apr 03, #3-5 May 03, #3-6 Jun 03, #3-7 Jul 03, #3-8 Aug 03, #3-9 Sep 03 #3-10 Oct 03, #3-11 Nov 03, #3-12 Dec 03, #4-1 Jan 04, #4-2 Feb 04, #4-3 Mar 04, #4-4 Apr 04, #4-5 May 04, #4-6 Jun 04, #4-7 Jul 04, #4-8 Aug 04, #4-9 Sep 04, #4-10 Oct 04, #4-11 Nov 04, #4-12 Dec 04, #5-1 Jan 05, #5-2 Feb 05, #5-3 Mar 05, #5-4 Apr 05 (see above)

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