Issue: Volume 7, Number 8
Date: August 2007
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, 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 If this newsletter prompts you to ask your own questions about DOE, please address them via mail

Many of you friends of Stat-Ease have emailed or telephoned us today about the terrible catastrophe last night — the collapse of a major bridge leading into downtown Minneapolis, only a short distance from our office. It is all over the news in the USA, but if you have not heard about this, see for
details and this link to CNN video obtained from a security camera on a nearby building: It shows one half of the span falling very precipitously and then, after a few
moments, the other half collapsing. As I came in to work just after dawn, a helicopter hovered directly overhead taking pictures from a discreet distance. All employees are now present or accounted for except one that went on vacation today, but I doubt very much that he or any of his family had the misfortune of being on the bridge when it fell—someone would have told us by now. Shari Kraber missed the collapse by only 10 minutes on her route home from the airport after attending the Joint Statistical Meetings this week in Salt Lake City. She heard the alert by radio in time to take an alternate route around downtown Minneapolis. Needless to say, Shari remains a bit rattled today, along with all the rest of us. However, we are getting on with business as best we can.

For an assortment of appetizers to get this Alert off to a good start, see these new blogs at
—One of the all-time achievements for engineering: Brunelleschi’s Dome
—Blowing up film takes on a whole new meaning (Part 2 : Statistical analysis)
—Blowing up film takes on a whole new meaning (Part 1 : Design of experiment)
—Drowning in statistics (featuring an original cartoon)

Also check out the thoughtful feedback to this blog:
—Tips of icebergs and humps of whales (1 comment, so far).

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

1. FAQ: For an interaction to be significant, must the lines cross?
2. Info Alert: Second edition of "DOE Simplified" book
3. Worldwide Alert: Interactive map leads to international network of experts on DOE, tutorial now in German and Korean
4. Info Alert: Publish your DOE success story — inspirational case-study articles sought for all industries!
5. Events Alert: Stimulating talks and demos by Stat-Ease
6. Workshop Alert: See when and where to learn about DOE

PS. Quote for the month: Two comments about scientific claims, one simply skeptical (from Sagan) and the other more cynical. (Page through to the end of this e-mail to enjoy the actual quote.)


1. FAQ: For an interaction to be significant, must the lines cross?

-----Original Message-----
From: Pennsylvania
"I am not familiar with the terminology 'interaction.' For example, when I see on the half-normal plot in your software that A, B and AB stand out as being significantly larger than all other effects, should I expect the lines on the interaction plot to be crossed?"

Answer (from Stat-Ease Consultant Wayne Adams):
"On the interaction plot the lines will be non-parallel. However, they do not need to cross on the plot to be a significant interaction."

Further comments:
My favorite interaction is the effect of time versus power on making microwave popcorn. At low power, changing time makes little difference, but when power is set high, watch out — the popcorn will burn! The lines on this interaction do not cross appreciably, however, they are significantly non-parallel. See Figure 3 at for example. On the other hand, two factors may depend utterly on each other and thus form an "X" cross-over on an interaction plot. An obvious example is the impact of background versus foreground on the readability of a video display, as you can see illustrated in
this article I wrote for Optical Engineering magazine (June/July 2005): Note that, although in a case like this, neither of the two main effects will appear significant, they are actually both quite important, but the effect of one factor will depend completely on the level of the other. Our software reminds users who drop parent terms from a significant interaction that they ought to put them back into their model. The reason stated is to preserve 'hierarchy,' but just do it as a practical matter.


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


2. Info Alert: Second edition of "DOE Simplified"

"DOE Simplified: Practical Tools for Effective Experimentation," co-authored by me and my colleague Pat Whitcomb is now available in its second edition from Productivity Press. For details, see This paperback book provides the basics of DOE for scientists, engineers and quality professionals who appreciate the power of statistics, but not all the dry details and derivations. Our goal in writing is to keep things simple and make them fun. Calculations for practice problems and follow-up experiments (use it or lose it!) are made easy by the accompanying software—a fully-functional educational version (for 180 days) of Design- Ease(R) 7.1. This major new revision of the software sets the stage for introducing the following tools for design and analysis of experiments:
—Pareto chart of effects benchmarked statistically to assess relative significance
—Minimum-run screening designs
—Multiple response optimization via desirability.

More importantly, we added a capstone chapter on the keys to setting up a good design of experiments and executing it successfully. The chapter details a four-step planning process for design of experiments, including assessment of statistical power. Due in large part to the Six Sigma quality movement, DOE has become much more prevalent in non-manufacturing areas since our first edition came out in 2000. Thus we shifted from the usual industrial example for our final case to a sales process involving a call center for customer service. As statistician Lynne Hare says "experimental design can lead to feelings of pure joy, especially when it points in the direction of improvement." Pat and I hope to share this joy with as wide an audience as possible. We believe you will find the new edition of "DOE Simplified" an easy read and one that will pay great dividends.


3. Worldwide Alert: Interactive map leads to international network of experts on DOE, tutorial now in German and Korean

See for a map of the world on which you can click your location for a quick link to our network of value-added resellers, most of whom are experts in their own right on DOE. Also, we are making some progress in translating key software tutorials by now providing one on two-level factorials in German. This tutorial is also available in Korean. These are posted at In addition, a number of our publications on DOE have been translated to Italian. See . These come from our international network of experts on DOE. Others have expressed interest in translating to additional languages—not an easy task for such a technical topic. We will keep you posted.


4. Events Alert: Stimulating talks and demos by Stat-Ease

Click for a list of 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 reimbursements for airfare, hotel and meals—expenses only. In any case, it never hurts to ask Stat-Ease for a speaker on this topic. Contact if you have an event coming up with an open slot for a presentation.


5. Events Alert: See when and where to learn about DOE

Seats are filling fast for the following DOE classes:

--> Experiment Design Made Easy (EDME)
(Detailed at
> August 21-23 (Minneapolis)
> September 18-20 (Philadelphia, PA—contact us for site)

--> Mixture Design for Optimal Formulations (MIX)
> August 7-9 (Minneapolis) SOLD OUT
> October 23-25, 2007 (Minneapolis)

--> Response Surface Methods for Process Optimization (RSM)
>September 25-27 (Minneapolis)

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. Quotes for the month—Two comments about scientific claims, one simply skeptical (from Sagan) and the other more cynical:

"Extraordinary claims require extraordinary evidence."
—Carl Sagan

"Most of the time, when you get an amazing, counterintuitive result, it means you screwed up the experiment."
—Professor Michael Wigler, Columbia University (resume at
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
—Stat-Ease consultants Pat Whitcomb, Shari Kraber and Wayne Adams (see for resumes)
—Statistical advisor to Stat-Ease: Dr. Gary Oehlert (
—Stat-Ease programmers, especially Tryg Helseth and Neal Vaughn (
—Heidi Hansel, Stat-Ease marketing director, and all the remaining staff


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 (see above)

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