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Vol: 15 | No: 1 | Jan/Feb '15
Stat-Ease
The DOE FAQ Alert
     
 

Stat-Ease Statistical Group

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 click here.

To open another avenue of communications with fellow DOE and Stat-Ease fans, sign up for The Stat-Ease Professional Network on Linked in. A recent posting features “Better Baseball Stats—visual representation using bat size”

 
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Topics in the body text of this DOE FAQ Alert are headlined below (the "Expert" ones, if any, delve into statistical details):

1:  Software alert: Version 9.0.4 of Design-Expert® software released (free update for licensed users of v9)—adds categorical factors to definitive screening designs
2:  FAQ: Where do I find general factorial designs in v9 of Design-Expert (DX9)?
3:  FAQ: How do I interpret the W statistic and associated p value shown on the half-normal plot of effects?
4:  Info alert: Application of DOE to a tricky welding problem
5: Webinar alert: Practical Strategies for Model Verification
6: Events alert: Where and when to attend talks by Stat-Ease and meet our experts
7:  Workshop alert: Mixture design classes coming to the East Coast!
 
 

PS. Quote for the month: Sage words from Box, Hunter & Hunter on the symbiosis between experimenters and statisticians.


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1: Software alert: Version 9.0.4 of Design-Expert® software released (free update for licensed users of v9)—adds categorical factors to definitive screening designs

Newly-released version 9.0.4 of Design-Expert software is posted at this download site for free trial evaluation.  To update older licensed versions of 9.0, simply download the update from within the program, or download the full installation and reinstall it.  The release primarily provides maintenance of existing features.  However, it also adds categorical factors to definitive screening designs (DSDs) as shown below.

Categoric Factors for DSD's
Screen shot showing new capability for adding categoric factors to definitive screening designs

View the Read Me file for details on this update, installation tips, known ‘bugs,’ change history, and FAQs.  If you have any questions about DSDs, email [email protected].

PS. Reminder: If you want to receive notice when an update becomes available, go to Edit on the main menu of your program, select Preferences and, within the default General tab, turn on (if not already on by default) the “Check for updates on program start” option.


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2: FAQ: Where do I find general factorial designs in v9 of Design-Expert (DX9)?

Original question from a Senior Research Scientist:
“The new DX9 version of your software no longer lists “General Factorial” on its Factorial tab.  I like this design and find it very easy to use.  The design-building wizard makes it very straightforward.  Is there any option in the new version which offers something similar to the general factorial?”

Answer from Stat-Ease Consultant Brooks Henderson:
“Yes.  We renamed some of the designs to make them more understandable to users that aren’t trained in DOE.  The “General Factorial” Design is now called “Multilevel Categoric”.  This is the same design builder as before, just renamed.  Here is a cheat sheet for all of the name changes we did from v8 to v9 and the newly added designs (in DX9 only).

Design Options in V8 vs V9

The new designs in DX9 are the definitive screen and a variety of split plots, including a multilevel categoric option (in addition to the completely randomized one), which comes in handy for dealing with “hard to change” factors such as oven temperature.  Also added is a “Simple Sample” choice for those who only want to generate statistics and plots for a single set of data, for example from a manufacturing line.”

P.S. For a detailing of all the new v9 features (not including the new DSD plus “cats” coming with v9.04), click the Features tab here. --Mark

(Learn more about factorial design by attending the two-day computer-intensive workshop Experiment Design Made Easy.  Click on the title 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: FAQ: How do I interpret the W statistic and associated p value shown on the half-normal plot of effects?

Original question from a Science and Technology Manager:
“I would like to know how to interpret the W statistic and associate p value shown by Design-Expert alongside [at upper left] its half-normal plot of factorial effects [example shown below].”

Half-Normal Plot

Answer from Stat-Ease Consultant Wayne Adams:
“The Shapiro-Wilk test compares the distribution of the unselected effects, to a normal distribution.  An insignificant result (p>0.1) indicates there is not enough evidence to conclude the unselected effects are not normally distributed.  If the test comes out significant, then one should examine the model selection, making sure that you haven’t over or under selected the model.

A significant result is not a reason to fail the graphical selection.  Continue on with the analysis tools provided by Stat-Ease software.  Pay attention to the ANOVA (analysis of variance) statistics.  If they do not stop you, then move on to the diagnostic plots.  There you may see non-normal residuals.  If so, let the diagnostics guide you to a remedy such as a transformation or dealing with outliers.

Think of the Shapiro-Wilk test as a mild warning, if significant, to pay extra attention to the diagnostic results.”

(Learn more about interpreting half-normal plots by attending the two-day computer-intensive workshop Experiment Design Made Easy.  Click on the title 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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4: Info alert: Application of DOE to a tricky welding problem

Last July at our European DoE User Meeting Chris Bertoni, Director of Quality and Technical Services at 4Front Engineered Solutions, presented a really interesting case study on the application of DOE to a tricky welding problem.  Welding Design & Fabrication posted his associated paper here.  Check it out!


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5: Webinar alert: Practical Strategies for Model Verification

In this webinar titled “Practical Strategies for Model Verification” (repeated three times for your scheduling convenience), our Stat-Ease Consultant Martin Bezener demonstrates tools in Design-Expert that put a chosen polynomial to the test.  Martin joined us in 2014, going full time upon completion of his graduate studies in statistics.  He brings a high level of expertise to this vital issue of determining whether a given model is fit for use.

Reserve your Webinar seat now at by clicking one of the links below:

  1. Monday, March 16 at 8 pm USA-CDT* for eastern Asia and Oceania (others welcome!),
  2. Wednesday, March 18 at 5:30 am USA-CDT* for Europe, Africa, Middle East and western Asia (others welcome!),
  3. Thursday, March 19 at 11 am USA-CDT* for the Americas and Caribbean (others welcome!).

If this is your first Stat-Ease webinar, please review these suggestions on how to be prepared.  If questions remain, direct them to our Communications Specialist, Karen Dulski, via [email protected].

*(Note that the USA goes on daylight savings time, “DT”, on March 8 this year—2015.  To determine the time in your zone of the world, try using this link.  We are based in Minneapolis, which appears on the city list that you must manipulate to calculate the time correctly.)


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6: Events alert: Where and when to attend talks by Stat-Ease and meet our experts

Click here for a list of upcoming appearances by Stat-Ease professionals—newly posted for the 2015 calendar year.  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 reimbursement for travel expenses.  In any case, it never hurts to ask Stat-Ease for a speaker on this topic.


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7: Workshop alert: Mixture design classes coming to the East Coast!

All classes listed below will be held at the Stat-Ease training center in Minneapolis unless otherwise noted.  If possible, enroll at least 4 weeks prior to the date so your place can be assured.  Also, take advantage of a $400 discount when you take two complementary 2-day workshops that are offered on consecutive days.

*Receive a $200 discount per class when you enroll 2 or more students or enroll in consecutive 2-day workshops. Receive a $100 discount for enrolling in the FSPD workshop along with another class.

** Take both MIX and MIX2 to earn $400 off the combined tuition!

See this web page for complete schedule and site information on all Stat-Ease workshops open to the public throughout 2015 (newly posted).  To enroll, scroll down to the workshop of your choice and click on it, or call Rachel Pollack 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].


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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.
2021 East Hennepin Avenue, Suite 480
Minneapolis, Minnesota 55413 USA

PS. Quote for the month—symbiosis between experimenters and statisticians:

 
"While experimenters can greatly gain from the use of statistical methods, the converse is even more true.”
—Box, Hunter & Hunter, Statistics for Experimenters, 2nd Ed.

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, Wayne Adams, Brooks Henderson, and Martin Bezener
—Statistical advisor to Stat-Ease: Dr. Gary Oehlert
Stat-Ease programmers led by Neal Vaughn
—Heidi Hansel Wolfe, Stat-Ease sales and marketing director, Karen Dulski, and all the remaining staff that provide such supreme support!

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DOE FAQ Alert ©2015 Stat-Ease, Inc.
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