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 previous DOE FAQ Alerts, 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.
Here's an appetizer to get this Alert off to a good start: See http://micro.magnet.fsu.edu/electromag/java/cd/index.html to learn how a compact disk works at the Molecular Expressions web site. Explore their acclaimed photo galleries featuring the fascinating world of optical microscopy.
Here's what I cover in the body text of this DOE FAQ Alert (topics that delve into statistical detail are designated "Expert"):
Seven steps for doing DOE successfully
the objective of the experiment: What specifically are you trying
a design that will give the desired amount of information in a reasonable
number of runs. In your initial design, try to identify all main effects
and as many interactions as you can within the restrictions on time,
material, cost and other resources.
It is likely to take two to three of these seven-step DOE cycles before you reach optimum processing conditions.
Stat-Ease offers expert consulting on DOE.* If you hire one of us (or whomever), here's how I recommend you proceed:
A. Have us
come on-site for one day to plan the details of the experiment. Some
up-front work can be done by your engineers before we get there, like
brain-storming on the variables and thinking about how the responses
can be measured.
*(See http://www.statease.com/consult.html for details on consulting services offered by Stat-Ease, Inc.)
"I have just joined a new company that isn't very statistically oriented. It offers online Internet services for which I believe DOE can be put to great use. I am keen to demonstrate the efficacy of DOE to the company so that it may be used consistently in the future. Therefore, I set up a seven-factor design with multiple categories per level using the free, trial-version of Design-Expert® software posted at your web site.*The experiment will track factors relating to profitabilityincluding price, trial period, type of incentive, etc. For the response, I take the percentage of users who cancel their subscription before the first payment period."
"My question is how can I tell how many replicates I will need to run in order to be able to distinguish between the main effects. Also, how should I go about entering those replicates? I am likely to have 70-200 distinct (paid/did not pay) data points per test cell. The only way I can currently see to do this is to replicate the entire row multiple times, but this is not practical for the number of replicates I am considering."
How large a sample will be needed depends on:
*(The free trial of Design-Expert can be downloaded from http://www.statease.com/soft_ftp.html.)
Sorry, due to the high cost of shipping, this offer applies only to residents of the United States and Canada: Send me an e-mail if you'd like a free copy of Box and Drapers' classic statistical text "Empirical Model-Building and Response Surfaces." Originally published in 1987 (John Wiley and Sons, New York), this book is a classic in the field of response surface methods (RSM) for process optimization. However, for workshops on this topic,* Stat-Ease now uses Myers and Montgomerys' "Response Surface Methods" (see this book and others listed for purchase via ecommerce at http://www.statease.com/prodbook.html).
*(Learn more about RSM by attending the three-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.)
Gain technical recognition in your company
and scientific field.
Share a DOE with our writer at: RABURNHAM@PublicationCoordination.com
Rename proprietary factors if needed to maintain confidentiality.
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!
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 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@StatEase.com
Mark J. Anderson, PE, CQE
PS. Quote for the
month: Inflammatory comments about statistics:
wanted: A chemist with a strong interest in DOE is looking for work
in central California.
Acknowledgements to contributors:
DOE FAQ Alert—Copyright 2004
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