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Issue:
Volume 10, Number 1 (Circulation: Over 5500 worldwide)
Date:
January 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 http://www.statease.com/doealertreg.html. If this newsletter prompts you to ask your own questions about DOE, please address them via mail to: [email protected].
Also, Stat-Ease offers an interactive web site—the Support Forum for Experiment Design at http://forum.statease.com. 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, http://www.StatsMadeEasy.net* (-> new web site!), and see a number of new blogs (listed below, beginning with the most recent one):
—Management blog carnival (organized by John Hunter)**
—Pushing the limits on alcohol levels for holiday cheer—higher the better (?)
—The State of happiness
—A journal title that caught my eye today
—Atlantic claws coming to town this Christmas
—STEM grads leaking outside their field
*Need a feed or e-mail updates from StatsMadeEasy? Go to http://feeds.feedburner.com/StatsMadeEasy. 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. Newsletter Alert: December issue of the Stat-Teaser announces the release of version 8 of Design-Expert® software
2. FAQ: Why am I told to recalculate the effects for half-normal plotting?
3. Expert-FAQ: Impossible levels in central composite design
4. Info Alert : Bioprocessing and Process Development
5. Book Giveaway: Winners announced
6. Events Alert: National Defense Industrial Association (NDIA) test and evaluation (T&E) conference
7. Workshop Alert: See when and where to learn about DOE
P.S. Quote for the month: DOE is about budget.*
*See accompanying heads up on LinkedIn groups specializing on design of experiments.
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1. Newsletter Alert: December issue of the Stat-Teaser announces the release of version 8 of Design-Expert® software
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 December issue at http://www.statease.com/news/news0912.pdf. It provides details on the release of version 8 of Design-Expert® software—the key features, as well as pricing for new or upgraded licenses (see order form on the last page).
This Stat-Teaser also features an educational article by Consultant Pat Whitcomb on the graphical selection of factorial effects. If you make use of two-level factorial design (or provide statistical advice to the experimenters), I urge you to read Pat's advice on picking effects from the handy half-normal graph, which now (in version 8) works for general factorials, that is, designs with factors having more than two levels.
Thank you for reading our Stat-Teaser newsletter. If you 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. (Note: You will be notified via the DOE FAQ Alert on new newsletter posts.) In any case, we appreciate you passing along hard copies and/or the link for the posting of the Stat-Teaser to your colleagues.
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2. FAQ: Why am I told to recalculate the effects for half-normal plotting?
-----Original Question-----
From: Glass chemist
"I've designed a 6-factor two-level (2^6) experiment with 8 center points (40 runs). Unfortunately, one of my samples got lost along the way. When I analyze the data, Design-Expert tells me that the design is not orthogonal, presumably because of the lost sample. It then tells me to ‘recalculate.’ When I do this my half normal plot looks different—often much better. Could you briefly explain what is going on? (I attended one of your training courses way back about 5 years ago, so the details of the calculation are a little hazy)."
Answer (from Stat-Ease Consultant Shari Kraber):
"Thanks for asking your question! With a 'perfect' DOE, all factor effects are calculated independently from each other—we say the design is orthogonal. When you lose a run, then the design becomes just slightly non-orthogonal and the effect calculations are now slightly dependent on what else is in the model. Design Expert is programmed with the math so that all the effects are estimated correctly in the ANOVA, whether or not you actually press that Recalculate button. Pressing the button allows you to see the adjustments on the half-normal graph and you can change your model if needed. Sometimes recalculating makes things more clear for decision-making and sometimes it doesn't. In any case, it is more accurate."
(Learn more about half-normal plots by attending the two-day computer-intensive workshop "Experiment Design Made Easy." See http://www.statease.com/clas_edme.html for a description of this class and link from this page to the course outline and schedule. Then, if you like, enroll online.)
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3. Expert-FAQ: Impossible levels in central composite design
-----Original Question-----
From: Research scholar
"I used Design-Expert software to design a standard (rotatable) central composite design (CCD) with three factors, which features an alpha value of 1.689 coded units for the axial points. However, for one factor the negative alpha value (-1.689) generates a negative value, which is physically impossible. Can I change this value to zero? How will this impact the design properties, for example the power?"
Answer (from Stat-Ease Consultant Wayne Adams):
"You can modify the design layout for your CCD by simply changing the negative amount to zero or above. It won't harm the design properties greatly even if you pull the value all the way in to the amount corresponding with the -1 coded value (low factorial level).
If your Design-Expert is version 7.13 or later (version 8 best!), you can check the impact of such modifications. Before making changes to the impossible factor-levels, click the Evaluation node, then click on the graph button. Take note of the Y-axis limits and fraction of design space (FDS) curve (how low and flat it appears). Then go back to the design layout, make the changes to the runs, and revisit the Evaluation graphs. If the FDS curve is still fairly low and flat, the changes will not ruin the analysis. If there is a substantial change, send your DX file to [email protected] and ask for some assistance."
PS. See an example of the v7.13 FDS plot posted at http://www.statease.com/files/FDS_help.pdf. Version 8 offers an additional feature not shown here—it calculates the FDS based on the half-width of the tolerance interval (TI).
(Learn more about central composite designs and FDS evaluation by attending the two-day computer intensive workshop "Response Surface Methods for Process Optimization." See http://www.statease.com/clas_rsm.html for a complete description. Link from this page to the course outline and schedule. Then, if you like, enroll online.)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4. Info Alert: Bioprocessing and Process Development
Jim Carey and Driss Elfahani of the Biomanufacturing Training and Education Center (BTEC) at NC State University presented a paper called "The Application of Statistical Design of Experiments for Mathematical Modeling of a Bacterial Cell Culture Process" before the NCSU Bioprocessing and Process Development Symposium. See their presentation posted at http://preview.tinyurl.com/ykkf34j.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
5. Book Giveaway: Winners announced
These lucky readers were drawn at random from over nearly 50 entrants. The copy of "Response Surface Methodology," 2nd edition, by Raymond H. Myers and Douglas C. Montgomery went to A.S. McKim, Technical Director, Gaylord Chemical, Bogalusa, LA. The two winners of "Statistical Intervals: A Guide for Practitioners," by Gerald J. Hahn and William Q. Meeker were:
-> Chris Nance, Six Sigma Black Belt, New Albany, IN
-> Mike Paulonis, Quality, Eastman Chemical, Kingsport, TN
Congratulations to these three winners and condolences to the others who entered into this drawing. Keep watching for more great books to be given away in the future.
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6. Events Alert: National Defense Industrial Association (NDIA) test and evaluation (T&E) conference
I will give a talk on "Optimal Verification Testing with Graphical Effects Analysis" and man the Stat-Ease exhibit at the National Defense Industrial Association (NDIA) National Test and Evaluation (T&E) Conference in San Diego on March 1-4. For details, see http://www.ndia.org/meetings/0910/.
Click http://www.statease.com/events.html 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 reimbursements for airfare, hotel and meals—expenses only. In any case, it never hurts to ask Stat-Ease for a speaker on this topic.
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7. Workshop Alert: See when and where to learn about 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!
—> Experiment Design Made Easy (EDME)
(Detailed at http://www.statease.com/clas_edme.html)
> February 9-10 (Minneapolis, MN)
> March 25-26 (King of Prussia, PA)
—> Designed Experiments for Life Sciences (DELS)
(http://www.statease.com/clas_dels.html)
> February 23-24 (Minneapolis)
> May 24-25 (San Francisco, CA)
—> Mixture Design for Optimal Formulations (MIX)
(http://www.statease.com/clas_mix.html)
> January 26-27 (Minneapolis)
> March 2-3 (Minneapolis)
—> Response Surface Methods for Process Optimization (RSM)
(http://www.statease.com/clas_rsm.html)
> April 29-30 (Minneapolis)
See http://www.statease.com/clas_pub.html 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 [email protected].
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I hope you learned something from this
issue. Address your general questions and comments to me at: [email protected].
PLEASE DO NOT SEND ME REQUESTS TO SUBSCRIBE OR UNSUBSCRIBE—FOLLOW THE INSTRUCTIONS AT THE END OF THIS MESSAGE.
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—DOE is about budget:
"DOE looks scary and expensive to a person guarding a budget because it proposes a set of trials to someone who may be thinking they could afford one more trial if they were sure it would give them the answer."
—Alan Corwin in a "DOE is About Budget" contribution to The Design of Experiment (DOE) Group on the LinkedIn professional network (http://www.linkedin.com). Other groups of interest for readers of DOE FAQ Alert might be the one sponsored by the American Society of Quality (ASQ) Statistics Division and, of course ;) the Stat-Ease Professional Network.
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 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, led by Neal Vaughn and Tryg Helseth
(http://www.statease.com/pgmstaff.html)
—Heidi Hansel Wolfe, Stat-Ease sales and marketing director, and all the remaining
staff that provide such supreme support!
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