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 http://www.statease.com/doealertreg.html. If this newsletter prompts you to ask your own questions about DOE, please address them via mail to:StatHelp@StatEase.com.
For an assortment of appetizers to get this Alert off to a good start, see these new blogs at http://statsmadeeasy.net:
1. FAQ: Too many blocks into too few runs each?
Answer (from Stat-Ease Consultant Shari Kraber):
PS from Mark: For a primer on blocking, see the March 2000 Stat-Teaser posted at http://www.statease.com/news/news0003.pdf. It details an experiment that my wife did with her preschool class on identification of dice as a function of the number of pips. The results, made possible by incorporating blocking in the experiment design, were a bit surprising.
PPS: The NIST/SEMATECH Engineering Statistics Handbook offers a neat explanation of blocking for two-level factorial designs at http://www.itl.nist.gov/div898/handbook/pri/section3/pri3333.htm.
P^3: For those who learn best by listening to a talking head, check out this free podcast by statistician Keith M. Bower at http://www.keithbower.com/DOE/Blocking%20in%20DOE.htm. (I enjoy the Scottish accent, perhaps mellowed a bit by Keith's stint in the midwestern USA as a student at the University of Iowa.)
"Block what you can, randomize what you cannot."
(Learn more about blocking by attending the three-day computer-intensive workshop "Experiment Design Made Easy." See http://www.statease.com/clas_edme.html 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. Reader Response: Breaking mixture design on beers into the individual blocks by taster to assess personal preferences
I got a lot of positive feedback* on my article detailing application of mixture design to optimal formulation of a beer cocktail (http://www.statease.com/news/news0709.pdf). I am happy to e-mail the data to anyone interested. Here is one exchange that relates to this month's FAQ on blocking.
You will see that Ben knew his brew—he liked the blend of Sam Adams Black Lager and Blue Moon (a ‘white’ wheat beer). In similar fashion you could break out the other experimental blocks individually. When I did this, I saw that my son-in-law Ryan, who hails from Milwaukee, liked Budweiser more than the other two tasters. After weaning him off milk, Ryan’s parents raised him on Miller Lite, so no wonder he preferred the bland Bud!
*PS. Here are a few outliers on the generally positive feedback. At the recent Fall Technical Conference of industrial statisticians I talked up my beer-cocktail mixture design to the fellow at my right at a speakers breakfast: Doctor mixture himself—John Cornell. He reminded me of his famous bar tending experiment detailed by "In Search of the Optimum Harvey Wallbanger Recipe via Mixture Experiment Techniques" in The American Statistician (Vol. 41, No. 3, Aug. 1987, pp. 190-194). Cornell told me that they had 15 workshop students participate in drinking varying blends of orange juice, vodka and Galliano. To limit the alcohol intake of any individual, the experiment was set up in a balanced incomplete block (BIB) structure per a design developed by Cochran and Cox in 1957, which limited the imbibing to three drinks each from a two-ounce jigger. These were randomly assigned as participants arrived at the post-workshop party. I could not top that! So then I turned to the statistician at my left, who was giving me a frown. Looking at her nametag, I noted she worked for Anheuser Busch of Saint Louis, the brewer of Bud. Oops! I suddenly wished my orange juice had a little kicker of vodka and Galliano.
3. Webinar Alert: Sizing RSM and Mixture Designs for Adequate Precision via use of Fraction of Design Space (FDS) Plots
You are invited to attend a free web conference by Stat-Ease on "Sizing RSM and Mixture Designs for Adequate Precision via use of Fraction of Design Space (FDS) Plots" at 8 AM Central USA Time on Wednesday, November 28 and again at 11 AM Thursday, November 29. See item number three in last month's DOE FAQ Alert for more details: http://www.statease.com/news/faqalert7-10.html. Attendance may be limited for one or both of these two one-hour webinar sessions. Contact our Communications Specialist, Karen Dulski, via email@example.com to sign up. 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
4. Book Giveaways: Winners announced
Three copies of the newly published second edition of "DOE Simplified," autographed by me and my co-author Pat Whitcomb were given away as promised by random drawing of postcards announcing version 7.1 of Design-Ease® and Design-Expert®. Here are the winners:
Congratulations to all!
(The two-part series of "Simplified" books on DOE and RSM can be ordered on line from http://www.statease.com/prodbook.html.)
5. Events Alert: Need a speaker on DOE?
Click http://www.statease.com/events.html 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 Mark@StatEase.com if you have an event coming up with an open slot for a presentation.
6. Workshop alert: Learn about DOE and get into the spirit of the season in Minneapolis (ideal weather for Mall shopping!)
Seats are filling fast for the following DOE class:
—> Experiment Design Made Easy (EDME) (Detailed at http://www.statease.com/clas_edme.html)
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 firstname.lastname@example.org.
I hope you learned something from this issue. Address your general questions and comments to me at: Mark@StatEase.com.
Mark J. Anderson, PE, CQE
PS. Quotes for the month—Why randomize? A cautionary note from George Box:
Acknowledgements to contributors:
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