Issue: Volume 6, Number 3
Date: March 2006
From: Mark J. Anderson, Stat-Ease, Inc. (

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

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Here's an appetizer to get this Alert off to a good start: See our new blog for lots of fun chat with a statistical/scientific/engineering bent. My profession of chemical engineers often refer to ourselves as 'comical en-grin-eers,' so be forewarned that the submissions to Stats Made Easy blog from me may be somewhat frivolous. Contributions from other statisticians at Stat-Ease, while less frequent, will likely be far more weighty. Feel free to comment on Stats Made Easy blogs. You may do this without entering your e-mail address. However, all entries are subject to my moderation of content considered abusive, illegal, defamatory, libelous, indecent, obscene, offensive, or threatening in any way. Many of you may make use of RSS (Really Simple Syndication) readers, which track and aggregate updates from your favorite web sites. As a user of Microsoft Outlook, I recommend RSS Popper freeware, which loads up quickly, is very intuitive to use and not too intrusive. You can download it from Then right-click on Stats Made Easy link to "Site Feed" and choose "Subscribe in RSS Popper" to be notified of new blogs from me or our statistical consultants at Stat-Ease. FYI, here are the select few blogs that divert my attention:
—Politically Incorrect Statistics
—Curious Cat Science and Engineering

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

1. FAQ: Why a p-value is not provided for variance from blocks
2. Info Alert: Review of DOE software favors Design-Expert®
3. Reader response: Getting the edge on Occam's Razor
4. Events alert: First European DOE User Meeting
5. Workshop alert: Crash Course on DOE for Sales & Marketing

PS. Quote for the month: Hunting for effects of practical importance that are statistically significant.


1. FAQ: Why a p-value is not provided for variance from blocks

-----Original Question-----
From: Cleveland, Ohio
"For the DOE with blocking effect, Stat-Ease software reports under ANOVA (analysis of variance) the Mean Square of the Block, but it doesn't calculate the F-value and associated probability (p-value). Why not?"

Answer (from Stat-Ease consultant Shari Kraber):
"One of the assumptions underlying the F test is the assumption of independence, which you get by complete randomization. Since blocking restricts randomization (by design), it violates this assumption. Thus, it wouldn't be proper statistically to perform the F-test. However, as a practical matter, here is my engineering 'rule of thumb': If the block mean square (MS) is four times larger than the residual MS, consider whatever you blocked out (for example: lot-to-lot, machine-to-machine, person-to- person, or day-by-day) to have a large enough effect that it bears investigating."

To add to what Shari says, I found this quote from the section on randomized complete block designs in the Second Edition of "Design of Experiments: Statistical Principles of Research Design and Analysis" by Robert O. Kuehl, Professor Emeritus at the University of Arizona ( "There is little interest in formal inferences about block effects, and the F statistic is generally not computed for this purpose even though it may appear in the output of a computer program." (page 270)

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


2. Info alert: Review of DOE software favors Design-Expert

-----Original Question-----
From: Quality Assurance Engineer in Wichita, Kansas "I am trying hard to buy Design-Expert version 7 (DX7) software, but I need some information from you guys. I began using DX software in 2003 and although I am convinced by any means to buy it for myself, I am having a hard time trying to convince my company that they should purchase corporate licenses. Please send me any information that will tell me how Design-Expert would be better for doing DOE than Minitab and other general statistics packages, as well as ones like yours that are dedicated to DOE."

For an unbiased assessment of design of experiment software, see the recent review in Scientific Computing World at

I like the bit where the author, Felix Grant, says that "Stat-Ease is known for the jokily accessible examples—a tradition continued in DX7's documentation with, for example, an experiment to discover whether Stat-Ease principal Mark Anderson can sleep longer in the morning without being late for work." :)

It's good to have some fun (in my opinion), but on a more serious note, Felix provides this telling observation on how Stat-Ease dedicates itself to providing the best program on the globe for design and analysis of experiments, which becomes possible only by not letting ourselves get sidetracked trying to supply all statistical tools for everyone: "DX7 would never be a replacement for a generic package. Nor does it try to 'function creep' into the territory of such a package. On the other hand, I've frequently encountered cases of a heavyweight analytic package being used to monitor simple descriptive measures for input and output values from a DoE system—and that is definitely using a shotgun to hunt crayfish."

Finally, the bottom line from this Scientific Computing World reviewer of DOE software is that he puts it to good use for his own consultancy: "All the projects into which I took DX7 over the past three months
yielded what the clients wanted—plus 107 unexpected but intriguing discoveries, at least a dozen of which look likely to spark new projects."

(For details on DX7 software, including "What's New—The Highlights," see Download a free, fully-functional 45-day trial of Design-Expert V7 at Pricing for new licenses and upgrades can be seen at the Stat-Ease e-commerce site:


3. Reader response: Getting the edge on Occam's Razor

Last month's DOE FAQ Alert* featured comments by Stat-Ease Consultant Wayne Adams on Albert Einstein's quote "Everything should be made as simple as possible, but not one bit simpler." Wayne's mention of Occam's Razor generated this exchange with Tom Scripps, a contract trainer for Stat-Ease (see Tom pictured at Tom asked, "Wayne—I am stumped for the moment—do you know why it's a razor?" Wayne answered, "Razor is a late English corruption of the Middle English 'rasor' which, used as a verb, is to cut off the non-essential. It has to do with razing your assumptions until bare explanation is left."

Coincidentally, Wayne sent me this heads-up: "I've been running some trials (not very scientific I'll admit) of my old razor [Gillette Sensor (two blades)] against the new Fusion Power (five blade, plus a sixth for 'close' work) that I bought last week. In terms of time to shave, closeness of the shave, nicks acquired during shaving, and number of shaves before performance declines, so far the Fusion is a cut above." Not only has Gillette gone crazy with this razor but also with their hyperbolic web site (warning: do not click this link unless you have a very fast internet connection and some time to kill!): Oh, and by the way, I bought the five-bladed Fusion and, like Wayne, feel that it works better than my old two-bladed razor—so much for the saying "the simpler, the better"!

*Back issues viewable below.


4. Events alert: First European DOE User Meeting

The "First European DOE User Meeting" for Design-Expert and Design-Ease Users" will be held at the Faculty Club in Leaven, Belgium on April 24 and 25. This DOE conference is sponsored by Stat-Ease with hosting by CQ Consultancy and participation from other European resellers of Design-Expert and Design-Ease software. See details at The meeting is a must for European users of Stat-Ease software and perhaps the perfect excuse for those elsewhere to take in the sights in Leuven and surroundings. I lunched at the city center some years ago—it was very beautiful!

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


5. Workshop alert: Crash Course on DOE for Sales & Marketing

(If you are a corporate technical professional, please pass this news on to your business people!) Quickly identify those factors which affect your sales and marketing results. Learn how they interact and apply that knowledge to make breakthrough increases in sales and profits. Attend the newly expanded two-day Crash Course on DOE for Sales & Marketing at the Stat-Ease training center in Minneapolis on April 19-20. See the course description and links to the syllabus and online enrollment at

See 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.


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—Hunting for effects of practical importance that are statistically significant:

"The effects plot flushes the birds and the stats shoot them down."

—Peter Fortini, Principal Statistician, Wyeth Biopharma, Andover, Maryland

This is a work in progress that came up as an ad lib during a teleconference on analysis of two-level factorials for ruggedness testing*—in particular the value of producing a half-normal plot of effects. Here's a thread of conversation I had with Peter afterwards. I said,"Peter, so far as I am concerned, you scored a direct hit by saying this. Is this something you made up on the spot, or did you hear it from someone else?" He said, "Actually, I just made it up on the spot—the recent story about our vice president crossed my mind at the moment. I think what I said or meant to say is 'the effects plot flushes the birds and the statistical test shoots at them.' The alternative wording is suggested because "shoot them down" has the implication that you succeed. A detail that is key to me is that when you shoot, it's a matter of chance whether you get a hit or miss (or bag your hunting companion! Now that you point it out, it really is a pretty good metaphor. If you hadn't captured it, I'd have forgotten, so this is more yours than mine." Do you readers have any suggestions for refining Peter's hunting metaphor?

PS. Wayne Adams adds this comment: "The half-normal plot always makes sure the birds flush out front, so you are less likely to pick-off the wrong target!"

*(See December Stat-Teaser cover-page article "Struggle for Power vs. Resolution vs. Simplicity in an ASTM Standard" 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
—Fellow 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 (see above)

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