Issue: Volume 10, Number 7 (Circulation: Over 5500 worldwide)
Date: July 2010
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:

Also, Stat-Ease offers an interactive web site — the Support Forum for Experiment Design at Anyone (after gaining approval for registration) can post questions and answers to the Forum, which is open for all to see (with moderation). Furthermore, the Forum provides program help for Design-Ease® and Design-Expert® software. Check it out and search for answers. If you come up empty, do not be shy: Ask your question! Also, this being a forum, we encourage you to weigh in!

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):

—A breadth of fresh error
—Tasty tidbits gleaned by a news-starved junky for stats trivia
—Bonferroni of Bergamo
—Priming R&D managers to allow sufficient runs for well-designed experiment

Also see the new comments on post #571 (6/6/10): "Bonferroni of Bergamo."

*Need a feed or e-mail updates from StatsMadeEasy? Go to It's easy!

"Your StatsMadeEasy blogs brighten up a dreary workday!"
—Applied Statistician, Florida

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

1. Program alert: V8.0.3 of Design-Expert® software released
2. FAQ: Box-Cox plot for diagnosing response transformations
3. FAQ: Central composite design calls for inoperable condition
4. Expert FAQ : How to expand a mixture contour plot that is constrained to a very narrow region
5. Reader contribution: Comparing Power of the DOE When Using Qualitative Variables Compared To Quantitative
6. Webinar Alert (2nd): DOE Made Easy and More Powerful via Design-Expert Software, Part 2 — Response Surface Methods (RSM) for Process Optimization
7. Events alert: Joint Statistical Meetings in Vancouver
8. Workshop alert: See when and where to learn about DOE, including a new 1-day class on Basic Statistics for DOE

P.S. Quote for the month: Embracing error.

(Page down to the end of this ezine to enjoy the actual quote.)


1. Program alert: V8.0.3 of Design-Expert® software released

Newly-released version 8.0.3 of Design-Expert® software is posted at for free trial evaluation. This web site also provides free patches to update older licensed versions of 8.0. View the ReadMe file for new features, installation tips, known 'bugs,' change history, and FAQs.


2. FAQ: Box-Cox plot for diagnosing response transformations

-----Original Question-----
Mattek Corp
"Is it correct to always apply the recommended response transformation derived from the Box-Cox plot? Or should other transformations be tried in order to improve the residual diagnostics?"

Answer (from Stat-Ease Consultant Shari Kraber):
"There is no 'always' rule in statistics. Whenever we try to make one, we'll find a data set that is contrary to the rule. However, I generally follow the Box-Cox recommendation for a transformation. Over time, I've built up a trust of the Box-Cox recommending the transformation that creates a significantly smaller error term. This generally produces a better model according to indicators such as the predicted R-squared."

PS from Mark: For a nice case where the Box-Cox plot proved to be providential, see "How to Use Graphs to Diagnose and Deal with Bad Experimental Data" by me and Pat Whitcomb posted at Also, I found a nice primer on the Box-Cox plot at iSixSigma: Follow this shortened link for their posting on this diagnostics tool, which in this case is put to good use for statistical process control (SPC).

(Learn more about transformations by attending the two-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.)


3. FAQ: Central composite design calls for inoperable condition

-----Original Question-----
Researcher at Nanyang Technology University in Singapore
"I intend to study enzyme concentration from 0 to 50 %(v/v). There are no issues when I study it under the full factorial design where three distinct points are studied (0, 25 & 50%). However, an issue arises when I augment it into central composite design: Some points fall outside of the original ranges. I believe these are the axial points. One of the points calls for a negative concentration (-17.04%)! Can I ignore this point? What other solutions may there be?"

Answer (Stat-Ease Consultant Wayne Adams):
"Feel free to pull the axial runs in so they stay within the area of operability. When building the axial block in Design-Expert, simply click on the options button. You are then presented with alternative choices such as one for a 'face centered' design, which sets the axial points to the original factorial range. You can also build the design with the default axial levels and manually type over the impossible condition(s), for example by entering zero (0) for the negative concentration."

PS from Mark: See some illuminating pictures of central composite design options at NIST/SEMATECH e-Handbook of Statistical Methods:

(Learn more about central composite designs by attending the two- day computer-intensive workshop "Response Surface Methods for Process Optimization." See for a complete description. Link from this page to the course outline and schedule. Then, if you like, enroll online.)


4. Expert FAQ: How to expand a mixture contour plot that is constrained to a very narrow region

-----Original Question-----
Material Scientist, Personal Care
"I have a set of odd data for a three-component system. Component A varies from 0.41 to 0.93, component B varies from 0.07 to 0.57, and component C varies from 0.00028 to 0.012. As you see, due to the very low percentage of component C, the contour is congested into a very thin strip along the border between A and B. How can I plot the contour with a very narrow range of component C to see the difference."

Answer (Stat-Ease Consultant Wayne Adams):
"The contour plot can be zoomed by Design-Expert to see a particular area of the graph. To zoom in, place the cursor in the graph area, left-click and hold and drag the cursor to draw a box around the area you want to zoom. Click the default button on the Factors tool to reset. If you zoom too much or to an area where there are no predictions (grey), an error message will appear: Click the default button to clear it. With version 8, you can also roll the mouse wheel, which will center the plot on the cursor and zoom in or out. This is very handy!

(Learn more about dealing with constraints by attending the computer-intensive two-day workshop "Mixture Design for Optimal Formulations." See for a complete description of this class. Link from this page to the course outline and schedule. Then, if you like, enroll online.)


5. Reader Contribution: Comparing Power of the DOE When Using Qualitative Variables Compared To Quantitative

-----Original Contribution-----
Arved Harding, Applied Statistics Group, Eastman Chemical Company
"I had a great webinar with some folks at our Jefferson, PA site where I used your Design-Expert tutorials on general factorials part 1 and 2. I wrote this short paper as a follow-up to that. You may have something written up on this somewhere, if so please let me know. I couldn't recall if you had. If you have not done so please feel free to take this paper as a very rough draft and write up something on the topic."

See this write-up by Arved on "Comparing Power of the DOE When Using Qualitative Variables Compared To Quantitative" at It's good food for thought from a self-styled "friendly, neighborhood statistician." (I can attest to him being a really nice and knowledgeable fellow!) Feel free to weigh in with your comments and/or suggestions as an off-shoot of this contribution by Arved. I really appreciate feedback like this — thanks Arved and all for sharing your expertise. — Mark

PS. On a somewhat related note, the Design of Experiment (DOE) Group on LinkedIn ( features an ongoing discussion on "Discrete factor DOEs" that was initiated by Brad Kahlbaugh. A number of people have weighed in on this, including Pat Whitcomb of Stat-Ease.


6. Webinar Alert (2nd): DOE Made Easy and More Powerful via Design-Expert Software, Part 2 — Response Surface Methods (RSM) for Process Optimization

Keeping it simple and making it fun, Stat-Ease is introducing an array of statistical methods for design of experiments (DOE) made easy and more powerful via version 8 of Design-Expert software:

—Two-level factorials for process screening, characterization and verification
—Response surface methods (RSM) for process optimization
—Multicomponent mixture design for optimal formulation.

I will present the second of this series of free webinars by working through case studies on RSM on Wednesday, July 14 at 2 PM USA Central Time* (CT). I will repeat this presentation on Thursday, July 15 at 8 AM. 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, via . If you can be accommodated, she will provide immediate confirmation and, in timely fashion, the link with instructions for our new web-conferencing vendor: GotoWebinar (see

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


7. Events alert: Joint Statistical Meetings in Vancouver

On August 1-4 the city of Vancouver hosts the largest gathering of statisticians held in North America who will gather for the Joint Statistical Meetings (JSM) of the American Statistical Association (AS). If you make it to JSM, please stop by Booth #109 and visit with the Stat-Ease representatives there.

Click for a list of upcoming appearances by Stat-Ease professionals. We hope to see you sometime in the near future!

PS. Do you need a speaker on DOE for a learning session within your company or technical society at regional, national, or even international levels? If so, contact me. It may not cost you anything if Stat-Ease has a consultant close by, or if a web conference will be suitable. However, for presentations involving travel, we appreciate reimbursement for travel expenses. In any case, it never hurts to ask Stat-Ease for a speaker on this topic.


8. Workshop alert: See when and where to learn about DOE, including a new 1-day class on Basic Statistics for 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! Also, take advantage of a $395 discount when you take two complementary workshops that are offered on consecutive days. All classes listed below will be held at the Stat-Ease training center in Minneapolis unless otherwise noted.

—> Experiment Design Made Easy (EDME)
(Detailed at
> July 27-28*

—> Response Surface Methods for Process Optimization (RSM)
> July 29-30*

* Take both EDME and RSM to earn $395 off the combined tuition!

—> Basic Statistics for DOE (SDOE)
> August 16 => Pairs nicely with MIX workshop! Ask for discount.
> September 28**

—> Designed Experiments for Life Sciences (DELS)
> September 29-30**

** Attend both SDOE and DELS to save $295 in overall cost.

—> Mixture Design for Optimal Formulations (MIX)
> August 17-18
> October 26-27***

—> Advanced Formulations: Combining Mixture & Process Variables
(MIX2) ( )
> October 28-29***

*** Take both MIX and MIX2 to earn $395 off the combined tuition!

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—Embracing error.

"Error is to be expected and not something to be scorned or obscured."

—Trevor Butterworth, editor of

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, Wayne Adams and Brooks Henderson (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 marketing director, Karen Dulski, 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, #9-08 Aug 09, #9-09 Sep 09, #9-10 Oct 09, #9-11 Nov 09, #9-12 Dec 09, #10-1 Jan 10, #10-2 Feb 10, #10-3 Mar 10, #10-4 April 10, #10-5 May 10, #10-6 June 10, #10-7 July 10 (see above)

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