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Issue:
Volume 7, Number 9
Date:
September 2007
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, 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:
—Calculators achieve ‘retro’ status—‘70’s style available
again from HP
—Making the most from unhappy events (discusses "the Anna
Karenina" (TAK) bias)
—Coming 'round the Smoky Mountains
—The challenge of dealing with statistical anomalies such as
bridge collapses
Topics in the body text of this DOE FAQ Alert are headlined below (the "Expert" ones, if any, delve into statistical details).
1. FAQ: Oh, oh! Dropped my flask on the floor! Now what?
2. Expert FAQ: Dr. Frankenstein rebuilds a fractional factorial
3. Webinar Alert: Learn about the factorial planning process
4. Info Alert: Details on DOE for telemarketers, and response
surface methods (RSM) for rubber and plastics
5. Job Opening: Stat-Ease seeks a DOE professional!
6. Events Alert: Talk at Euro stats conference
7. Workshop Alert: See when and where to learn about DOE
PS. Quote for the month: Addicted to "DX." (Page through to the
end of this e-mail to enjoy the actual quote.)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1. FAQ: Oh, oh! Dropped my flask on the floor! Now what?
-----Original Message-----
From: New York State
"I was wondering what the ramifications were if you botch a run—say you dropped the flask on the floor and were not running any
replicates of that flask. Obviously, you can delete that line
from your design, but how much will that compromise the rest of
the results?"
Answer (from Stat-Ease Consultant Wayne Adams):
"What happens to your design depends on the base design and
which point you lose. For fractional factorial designs this
will be one of the corners. Often this will result in a two-factor interaction being aliased with everything. The best way to
tell is to leave the data missing (if no response could be
measured) or ignore the result in question, and then use the
design evaluation tool in your Design-Ease® or Design-Expert® software to see what information is lost.
Never delete an entire run—instead use the ignore feature in
your program's design layout. (I also urge you to make use of the
Notes node to record why a particular value is set to ignored
status.) Mathematically, any of the following options offered by
Stat-Ease software will produce the same model:
—Ignore (via right-click to Cell Status and change from
Normal),
—Leaving the cell blank (missing), and
—Delete row (via right-click on button to left)
However, it's always best to preserve the factor levels and
measured response value (if any) by setting individual cells or
the entire run to be ignored (shown lined out by 'strike-through'
in the software's display of the design layout)."
—Wayne
Further comments:
I cannot resist telling this related anecdote. Years ago I worked
as a process development engineer in a specialty-chemical research
center. I had the great fortune of working in a department
that encouraged use of statistically designed experiments and
provided on-the-job training on these powerful tools. However,
some of the chemists lacked enthusiasm for DOE. I arm-twisted one
into running a two-level factorial on processing conditions at the
bench prior to me scaling it up for pilot-plant studies.
Analyzing his data, I found an extreme outlier, which upon
inspection of the lab notebook, was described thusly: "I initiated
the reaction successfully, but the alarm went off for a fire drill
and I accidentally knocked the beaker to the floor. Half an hour
later I picked out the glass, transferred the viscous mass to
another beaker and resumed the reaction." I deemed this a special
cause and replaced the outlier (exceedingly low for yield!) with
an imputed value—the old-fashioned approach for dealing with
missing data. Thank goodness for dedicated DOE software and
computers capable of dealing better with incomplete test matrices.
—Mark
(Learn more about dealing with apparent outliers 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. Expert-FAQ: Dr. Frankenstein rebuilds a fractional factorial
-----Original Message-----
From: "Your Friendly, Neighborhood Statistician" Arved Harding"
I was doing some interesting design stuff today with version
7.1 of Design-Expert (DX). I felt like Dr. Frankenstein after
seeing the new feature that changes colors on the factorial design
builder when you change the number of blocks in the factorial.
[For example, adding blocks may degrade the resolution from
'green' resolution V to 'yellow' resolution IV.] I was playing
with our old buddy the 2^5-1 design. The default generators in DX
are I = ABCE and Block=ABD. This causes you to have 3 two-factor
interactions (2FI) confounded with other 2FIs. I found an NBS
Standard from 1957 that used as the default I=ABCDE and Block =AB.
So you only lose one interaction this way. I realize that
confounding interactions with one another is not as serious as
confounding interactions with Block, however you only lose one
interaction if you chose this design. If you have two factors
that can't logically interact, then this may be a better design."
Answer (from Stat-Ease Consultant Pat Whitcomb):
"Dear Dr. Frankenstein, Thanks for the feedback and suggestions;
glad you're enjoying yourself! We once used a 2FI for the block
generator; then minimum aberration came along. In minimum
aberration the lowest order terms are the most important and get
aliased with the higher order terms. The order is that ME is a
1, a 2FI is 2, a 3FI is 3, etc. with blocks being a 1.5.
Therefore having a block term generated by a 3FI (the new scheme)
rather than a 2FI (the old scheme) is lower aberration.
Having thought about this for a bit it makes sense to me. (My
first reaction was identical to yours.) Let's say AB is used to
generate blocks; and there is a significant AB effect. The block
effect now has a random component (whatever was blocked on) and a
fixed component (AB). If the AB effect is interpreted as a
blocking problem, time is spent trying to determine why the blocks
(machines, lots, operators or the like) are different and the fact
there is a significant 2FI is missed. Using ABD to generate
blocks gives some assurance the block mean square (MS) is due to
what was blocked on and isolates the 2FIs. Hopefully, you get
some idea about the existence of 2FIs, even if they can't be
positively identified. So, in the end, I bought into the
definition for minimum aberration."
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3. Upcoming Webinar: Learn about the factorial planning process
You are invited to attend a free web conference by Stat-Ease on "A Factorial Design Planning Process" at 8 AM and 11 AM USA
Central Daylight Time (CDT) on Wednesday, September 19.* It will
be based on a talk presented at last year's Fall Technical
Conference (FTC), which is jointly sponsored by American Society
of Quality (ASQ) Chemical & Process Industries Division, the ASQ
Statistics Division, and the American Statistical Association
(ASA) Sections on Physical and Engineering Sciences and Quality
and Productivity. Stat-Ease Consultant Shari Kraber, who co-presented with Pat
Whitcomb, reported afterwards that: "The Fall Technical Conference was attended by about 200
people; a small, but highly-influential group of industrial and
academic statisticians. We presented the talk, which provides a
structure for planning designs and incorporates our new up-front
power calculations. Lots of positive comments were given afterwards. Another speaker was so intrigued by our unique
minimum resolution V (MR5) designs that he added a citation to
his own presentation, triggering an interested reaction out of
that audience as well."
Attendance may be limited for one or both of the two one-hour long
webinar sessions on "A Factorial Design Planning Process."
Contact me via [email protected] to sign up. If you can be
accommodated, I will send you the link for the WebConnect and
dial-in for ConferenceNow voice via telephone. Toll-free access
extends world-wide, but not to all countries. Details will be
provided as needed.
Here is the talk's description provided by Shari and Pat to FTC
attendees:
Purpose: To present a specific process to organize and plan a
designed experiment, taking into consideration the power of the
design relative to the size of the effects.
Abstract: Newcomers to factorial design find it difficult to
choose appropriate designs with adequate power. In this
presentation, we introduce a clear process to determine the best
design that fits the problem. A discussion of statistical power
will show attendees how the size of the effect relative to the
noise is a critical criterion in design selection. We will also
discuss how to choose the ranges for the input factors, the
importance of evaluating aliases, and checking runs for safety.
Various case studies will illustrate the importance of using this
process to avoid DOE failure due to an incorrect design choice.
Attendees will take away a clear strategy for determining which
factorial design is appropriate for their data analysis needs.
*Argghh! Mark, here, being a bit of a buccaneer throwing a marlin
spike into the works of this here webinar: It sails on "Talk Like
a Pirate Day" (http://www.talklikeapirate.com/), so if my
Stat-Ease mateys say such things as "Avast, ye stat-lubbers, keep
a sharp eye for yonder optimum—thar be the treasure!" do not
jump overboard! ;)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4. Info Alert: Details on DOE for telemarketers, and response
surface methods (RSM) for rubber and plastics
Two new articles on statistical tools for design of experiments
are now available for your educational purposes.
Bob Gahagan, an independent consultant operating out of Columbia,
South Carolina, gave Stat-Ease permission to post an inspiring
article on DOE for telemarketers that you will find at
http://www.statease.com/pubs/doe_for_telemarketers.pdf.
In the Technical Notebook of their August 20th issue, Rubber And
Plastics News (http://www.rubbernews.com) published an article by
me titled "Response Surface Methods for Peak Process Performance."
See my text at http://www.statease.com/pubs/rubplast3_rsm.pdf.
This primer on RSM is the third in a series on DOE dating back a
decade,* which I wrote (with Pat Whitcomb's help) by invitation
from editor Harold Herzlich. He says "The object is to help
rubber-industry technical people understand and more fully utilize
the more efficient design of experiment (DOE) statistical
techniques that are developing. I have found many rubber industry
not aware of the way new software can take the pain out of the
process while helping design and evaluate multi-factor research,
development or industrial studies."
*Others are:
—"Breakthrough improvements with experiment design" published
in June 1997, see http://www.statease.com/pubs/plastics.pdf for
the original manuscript
—"Mixture DOE uncovers formulations quicker" published on
October 21, 2002, see http://www.statease.com/pubs/mixdoe.pdf
PS. In last month's DOE FAQ Alert I announced publication of the
second edition of "DOE Simplified." The link I provided went
directly to the publisher—Productivity Press of New York City.
I am pleased to see that it has now been picked up by ASQ's
Quality Press and posted at their web site. Go to
http://www.statease.com/doe_simp.html for details on this fun, but
very informative primer on DOE, and link from there to purchase it
online.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
5. Job Opening: Stat-Ease seeks a DOE professional!
Stat-Ease, Inc., a Minneapolis-based DOE software, training and
consulting company, has a permanent, full-time opportunity for an
energetic person to join our team. The position is a combination
of technical development and teaching. Job responsibilities
include teaching design of experiments workshops, providing
statistical support to clients, defining test cases for
statistical software development, researching statistical methods
for future software implementation, conveying statistical concepts
to programmers, writing/editing technical materials, and other
duties based on experience. This is a full-time, permanent
position in Minneapolis, MN with approximately 25% travel.
Minimum qualifications:
—Chemical or Biological or related Engineering degree with
5-10 years experience
—Strong math skills
—Aptitude and desire to learn more about how statistics can
improve products and processes
—Proven ability to turn concepts into solutions
—Hands-on DOE experience, mixture design desirable
—Teaching experience and strong ability to communicate with
technical professionals
—Excellent English skills—verbal and written
—US citizenship required
Resumes should be sent to [email protected].
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
6. Workshop alert: See when and where to learn about DOE
Seats are filling fast for the following DOE classes:
Experiment Design Made Easy (EDME)
(Detailed at http://www.statease.com/clas_edme.html)
—September 18-20 (Philadelphia, PA)
—October 9-11 (Minneapolis, MN)
Mixture Design for Optimal Formulations (MIX)
(http://www.statease.com/clas_mix.html)
—October 23-25 (Minneapolis)
Response Surface Methods for Process Optimization (RSM)
(http://www.statease.com/clas_rsm.html)
—September 25-27 (Minneapolis) **SOLD OUT**
—November 13-15 (Minneapolis) — added to accommodate overflow
from September class — seats available!
DOE for DFSS: Variation by Design (DDFSS)
(http://www.statease.com/clas_ddfss.html)
—November 7-8 (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].
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. Quotes for the month—Addicted to "DX":
(Note: A technical manager at General Electric said his employees
are "addicted" to Design-Expert ("DX"), thus precipitating a
renewal of their annual network license to satisfy their
addiction. Our resident punster, Tryg Helseth, was moved by this
news to adapt the lyrics to a popular song. —Mark)
Addicted to DX
by Tryg Helseth (with apologies to Robert Palmer*)
"Your computer's on, you're data's in
Your mind is lost amidst the din
Your palms sweat, your keyboard shakes
Another transform is what it takes
You can't sleep, you can't eat
You have runs you must repeat
You squeeze the mouse, it starts to squeak
A new analyses will look less bleak
Whoa, you like to think that you're immune to the stats, oh yeah
It's closer to the truth to say you need your next fix
You know you're gonna have to face it, you're addicted to Dee Ex"
* Author of lyrics at http://users.cis.net/sammy/addicted.htm
Trademarks:
Design-Ease, Design-Expert
and Stat-Ease
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, especially Tryg Helseth and Neal Vaughn
(http://www.statease.com/pgmstaff.html)
—Heidi Hansel, Stat-Ease marketing director, and all the remaining
staff
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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