Issue: Volume 9, Number 7
Date: July 2009
From: Mark J. Anderson, Stat-Ease, Inc., Statistics Made Easy® Blog

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 the previous DOE FAQ Alert, see below.

==> Tip: Get immediate answers to questions about DOE via the Search feature on the main menu of the Stat-Ease® web site. This not only pores over previous alerts, but also the wealth of technical publications posted throughout the site.

Feel free to forward this newsletter to your colleagues. They can subscribe by going to If this newsletter prompts you to ask your own questions about DOE, please address them via mail to:

For an assortment of appetizers to get this Alert off to a good start, follow this link,* (-> new web site!), and see a number of new blogs (listed below, beginning with the most recent one):

—Does good experimental design require changing only one factor at a time (OFAT)?
—"Decisions taken by statistical professionals are final"
—Rabid for numbered bones
* Need a feed from StatsMadeEasy to Microsoft's Outlook? See

Also, Stat-Ease offers an interactive web site — its Support Forum for Experiment Design at Whereas this monthly ezine — the DOE FAQ Alert — shares one-on-one communications with Stat-Ease StatHelp, anyone (after gaining approval for registration) can post questions and answers to the Forum, which is open for all to see (with moderation). Check it out and weigh in!

Topics in the body text of this DOE FAQ Alert are headlined below (the "Expert" ones, if any, delve into statistical details).

1. Newsletter Alert: June issue of the Stat-Teaser features a fun, in-class experiment on paper clips; and a primer on determining sample size for a binomial response, such as pass/fail
2. Value-added reseller 'heads-up': Boston Software Group announced as Stat-Ease VAR in support of client throughout NE USA
3. FAQ: How do I detect statistical outliers in my experimental results?
4. Info Alert : Articles on mixture design and RSM for DFSS
5. Webinar Alert: Analyzing historical data
6. Reader Contribution: A DOE roadmap
7. Events Alert: Talk on practical considerations for optimal design slated for presentation in Sweden this September
8. Workshop Alert : Summer is a great time to tool up on DOE!

P.S. Quote for the month: An interesting reaction to a scientific discovery.


1. Newsletter Alert: June issue of the Stat-Teaser features a fun, in-class experiment on paper clips; and a primer on determining sample size for a binomial response, such as pass/fail

Many of you have received, or soon will, a printed copy of the latest Stat-Teaser, but others, by choice or because you reside outside of North America, will get your only view of the June issue at It features an article showing how a "Paper Clip Experiment Illustrates Statistical Design Principles."

If you deal with binomial responses such as pass/fail, be sure to page ahead to a detailing of the Stat-Ease "Power Calculator for Binomial Responses," laid out in the form of a Microsoft Excel spreadsheet by Consultant Wayne Adams in collaboration with Pat Whitcomb. This provides an extremely handy way to determine sample size per run in a designed experiment.

Thank you for reading our Stat-Teaser newsletter. If you do get the hard copy, but find it just as convenient to read what we post to the Internet, consider contacting us to be taken off our mailing list, thus conserving resources. However, we do appreciate you passing around hard copies of the Stat-Teaser, so do not feel obliged to forego this.


2. Value-added reseller 'heads-up': Boston Software Group announced as Stat-Ease VAR in support of client throughout NE USA

Our June Stat-Easer announces our new partnership with Boston Software Group of Boston, MA to market Stat-Ease software and training in the Northeast region (extending as far West as MI and OH) of the United States.Boston Software Group has over 40 years of combined sales, marketing and technical experience in the experimental design and exploratory data analysis markets, making them well-equipped for this new role. Boston Software Group’s customers include worldwide market leaders in numerous industries such as Merck, ExxonMobil, IBM, Genentech, United Technologies, and American Express.

If you are a Stat-Ease customer in this region, we think you will find it both convenient and beneficial to work with the knowledgeable Boston Software Group team. They look forward to meeting you and providing local support. Be assured that free technical support and limited free statistical support is still provided to you by Stat-Ease. As always, you are welcome to come to us directly for any reason. We greatly appreciate your business!


3. FAQ: How do I detect statistical outliers in my experimental results?

-----Original Question-----
Pharmaceutical chemist
"It's amazing how you detected a result that was accidentally typed incorrectly (numbers transposed). The model works far better with this data ignored! However, it would be helpful to know in the future on what I should look for as far as outliers are concerned."

Answer (from Stat-Ease Consultant Wayne Adams):
"Outliers are identified on the Externally Studentized Residuals plot (formerly called the Outlier t plot). On this plot observations that are not fit well by the other points stand out. Further identification of influential points are identified on the Leverage, DFFITS and DFBETAS plots. If a score appears different on these plots it indicates that run needs to be checked. Something is different about that point. Either the run was set up incorrectly, the observation was measured incorrectly, or a new discovery has been made. If you can assign one of the first two causes then you can safely remove the outlier. Often the special cause was a particular run pushed too hard on the envelope and left the population of good runs — my colleague Pat calls this 'falling off the operating table'."

Hmmm, that last bit is gruesome, but being overly aggressive at times when I experiment, it's something I can relate to. For more details on this subject, see "How to Use Graphs to Diagnose and Deal with Bad Experimental Data" by me and Pat (the manuscript for an article published in Quality Engineering) posted at Follow up on this by viewing the slides from Pat's August 2008 webinar on diagnostics at

(Learn more about outliers by attending the three-day computer- intensive workshop "Experiment Design Made Easy." See for a description of this class and link from this page to the course outline and schedule. Then, if you like, enroll online.)


4. Info Alert: Articles on mixture design and RSM for DFSS

Two case-study articles on DOE merit attention this month. Zivorad R. Lazic, author of "Design of Experiments in Chemical Engineering: A Practical Guide," collaborated with me to detail "Optimal Blending via Statistical Design of Experiments (DOE) Tailored to Formulation," which you can view at A statistically-based design of experiments (DOE) approach developed specifically for mixtures was used to formulate a blend of rayon fibers for a consumer product.

The other article is "Response Surface Methods (RSM) Achieve Design for Six Sigma (DFSS) Goals for Medical Device Manufacturing," which explains how engineers at a major medical device manufacturer used RSM to successfully model a key process for their flagship product. The RSM model then became the foundation for development of robust specifications to ensure quality at six sigma levels. See this case study posted at

*See Lazic's book described at this publisher web site:


5. Webinar alert (1st): Analyzing historical data

You are invited to attend a free web conference by Stat-Ease Consultant Pat Whitcomb on "Analyzing Historical Data." This free conference, which Pat will present at an intermediate level statistically, will be broadcast on Wednesday, September 15th at 2 PM USA Central Time* (CT). He will repeat his webinar on Thursday, September 16th at 8 AM. It is aimed at those who need help in trying to make any sense out of pre-existing data using regression modeling. As Pat will point out, there are many perils and pitfalls to watch for when working with happenstance data. Stat-Ease webinars vary somewhat in length depending on the presenter and the particular session — mainly due to breaks for questions: Plan for 45 minutes to 1.5 hours, with 1 hour being the target median.

When developing these one-hour educational sessions, our presenters often draw valuable material from Stat-Ease DOE workshops. Attendance may be limited, so sign up soon by contacting our Communications Specialist, Karen Dulski, via . If you can be accommodated, she will send you the link for the WebConnect and dial-in for ConferenceNow voice via telephone (toll-free access extends worldwide, but not to all countries).

*(To determine the time in your zone of the world, try using this link: Note that we are based in Minneapolis, which appears on the city list that you must manipulate to calculate the time correctly. It seems that figuring out the clock on international communications is even more complicated than statistics! Good luck!)


6. Reader Contribution: A DOE roadmap

-----Original Message-----
John Dubuc, ROI Creations, LLC, Scottsdale, AZ
"Hello Mark, would you be interested in publishing my DOE Roadmap in your newsletter? It addresses many FAQs including the ones you recently wrote* on confirmation runs."
*(June DOE FAQ Alert. #2)

See this information-packed flowchart posted at
Thank's John!


7. Events Alert: Talk on practical considerations for optimal design slated for presentation in Sweden this September

Pat Whitcomb will deliver a talk on practical considerations for optimal design at the annual conference of the European Network for Business and Industrial Statistics (ENBIS), which will be held September 20-24 in Goteborg, Sweden. For details on this event, see Click for a list of upcoming appearances by Stat-Ease professionals. We hope to see you sometime in the near future!


8. Workshop Alert: Summer is a great time to tool up on DOE!

Seats are filling fast for the following DOE classes. If possible, enroll at least 4 weeks prior to the date so your place can be assured. However, do not hesitate to ask whether seats remain on classes that are fast approaching!

—> Response Surface Methods for Process Optimization (RSM)
> July 7-9 (Minneapolis, MN)
> December 1-3 (Minneapolis)

—> Mixture Design for Optimal Formulations (MIX)
> August 11-13 (Minneapolis)
> October 27-29 (Minneapolis)

—> Experiment Design Made Easy (EDME)
(Detailed at
> August 18-20, 2009 (Minneapolis)
> November 3-5, 2009 (Minneapolis)

—> DOE for DFSS: Variation by Design (DDFSS)
> November 10-11, 2009 (Minneapolis)

—> Designed Experiments for Life Sciences (DELS)
> Fall 2009 (Cambridge, MA)

See for complete 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 Elicia at 612.746.2038. 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.*

*Once you achieve a critical mass of about 6 students, it becomes very economical to sponsor a private workshop, which is most convenient and effective for your staff. For a quote, e-mail


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




Mark J. Anderson, PE, CQE
Principal, Stat-Ease, Inc. (
2021 East Hennepin Avenue, Suite 480
Minneapolis, Minnesota 55413 USA

PS. Quote for the month —An interesting reaction to a scientific discovery:

"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka' but 'That's funny...'"

—Isaac Asimov

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

Acknowledgements to contributors:
—Students of Stat-Ease training and users of Stat-Ease software
—Stat-Ease consultants Pat Whitcomb, Shari Kraber and Wayne Adams (see for resumes)
—Statistical advisor to Stat-Ease: Dr. Gary Oehlert (
—Stat-Ease programmers, led by Neal Vaughn and Tryg Helseth (
—Heidi Hansel Wolfe, Stat-Ease sales and marketing director, and all the remaining staff that provide such supreme support!


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, #5-5 May 05, #5-6 Jun 05, #5-7 Jul 05, #5-8 Aug 05, #5-9 Sep 05, #5-10 Oct 05, #5-11 Nov 05, #5-12 Dec 05, #6-01 Jan 06, #6-02 Feb 06, #6-03 Mar 06, #6-4 Apr 06, #6-5 May 06, #6-6 Jun 06, #6-7 Jul 06, #6-8 Aug 06, #6-9 Sep 06, #6-10 Oct 06, #6-11 Nov 06, #6-12 Dec 06, #7-1 Jan 07, #7-2 Feb 07, #7-3 Mar 07, #7-4 Apr 07, #7-5 May 07, #7-6 Jun 07, #7-7 Jul 07, #7-8 Aug 07, #7-9 Sep 07, #7-10 Oct 07, #7-11 Nov 07, #7-12 Dec 07, #8-1 Jan 08, #8-2 Feb 08, #8-3 Mar 08, #8-4 Apr 08, #8-5 May 08, #8-6 June 08, #8-7 July 08, #8-8 Aug 08, #8-9 Sep 08, #8-10 Oct 08, #8-11 Nov 08, #8-12 Dec 08, #9-01 Jan 09, #9-02 Feb 09, #9-03 Mar 09, #9-04 Apr 09, #9-05 May 09, #9-06 June 09, #9-07 July 09 (see above)

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