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:[email protected]. For an assortment of appetizers to get this Alert off to a good start, see these new blogs at http://statsmadeeasy.net: 1. FAQ: Responses that cannot be easily quantified ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1. FAQ: Responses that cannot be easily quantified -----Original Message----- Answer (from Stat-Ease Consultant Wayne Adams): "Yes, the responses must be numeric so a model can be fitted for predictive purposes and statistically validated. Actual counts would be best, but if this cannot be easily done, measure the amount of bacteriological growth with a rating scale. The more discrete levels you can assign the better, assuming an expert can discern the difference between ranks on a consistent basis. For greater accuracy and precision, take a series of photographs and create a template for rating according to the scale. Have the same person(s), preferably someone experienced in the field, rate the growth—the more observers, the better to reduce measurement error by the power of averaging. It's best that the actual experimenter not do the rating—keep the observers blind to the factor settings to avoid bias. Also, randomly present the material to the observer(s) to counteract any aging effects on the experimental samples." More from me: (Learn more about entry-level aspects of DOE 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. FAQ: Non-orthogonal design matrices -----Original Question-----
From: Switzerland "I introduced an experimental design which was not orthogonal (independent variables were correlated) in your Design-Expert software and I got a predictive model. How do I assess the individual effects?" Answer (from Stat-Ease Consultant Wayne Adams): "Go to the design evaluation node in Design-Expert and view the variance inflation factor (VIF) results for the terms in your selected model. The ideal VIF is 1, which indicates orthogonality, that is, no correlation of that term with any others. As a rough rule, only if VIF's increase to 10 or more should you have cause for alarm that coefficients will be poorly estimated due to multicollinearity." More from me: (Learn more about design evaluation by attending the three-day computer-intensive workshop "Response Surface Methods for Process Optimization." For description of this class, see http://www.statease.com/clas_rsm.html and then link from this page to the course outline and schedule. If you like, enroll online.) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 3. Info Alert: Case study authors wanted—gain name recognition for you and your company by achieving publication Gain technical recognition in your company and scientific field by writing up your DOE success story for publication in a technical magazine and/or Internet web site. We can put you in touch with technical writers who specialize in articles like this and know how to get them placed. Rename proprietary factors if needed to maintain confidentiality. A thirty-minute interview, some e-mails, a review, and it's done! For more information, contact Heidi Hansel at [email protected]. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 4. Events Alert: Technical talks on DOE—speakers available! 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 [email protected] if you have an event coming up with an open slot for a presentation. 5. Workshop Alert: See when and where to learn about DOE
See http://www.statease.com/clas_pub.html 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 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.* *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].
Sincerely, Mark Mark J. Anderson, PE, CQE PS. Quote for the month — "Test all things; hold fast what is good." Acknowledgements to contributors: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Interested
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