Steve --
Your students are asking the good questions!! This comes up
repeatedly.
I try to minimize reference to unfamiliar statistical terms when
I introduce students to the use of Prediction/Regression/Linear Models
in science research projects. Without using special, unfamiliar terms
such as "reducing variation","blocking","confounding","main effects"
,etc. students can understand natural language statements, such as:
(Consider Example 10.22, page 774 of M&M 2nd edition)
1. "Is there a difference between the MEAN HEART RATE AFTER 6 MINUTES
OF TREADMILL EXERCISE of RUNNERS WHO AVERAGED AT LEAST 15 MILES PER WEEK and
a GROUP OF "SEDENTARY" SUBJECTS?
A shorthand might be the following ONE expression:
Is MEAN PERFORMANCE OF THE EXERCISE GROUP = MEAN PERFORMANCE OF THE "COUCH POTATOES"?
or, equivalently
Is MEAN PERFORMANCE OF THE EXERCISE GROUP - MEAN PERFORMANCE OF THE "COUCH POTATOES =
0"?
And after an interesting discussion about the problem, students might turn to:
2. "Is there a difference between the MEAN HEART RATE AFTER 6 MINUTES
OF TREADMILL EXERCISE of RUNNERS WHO AVERAGED AT LEAST 15 MILES PER WEEK and
a GROUP OF "SEDENTARY" SUBJECTS AND WHO ARE OF THE SAME SEX?
A shorthand might be the TWO expressions:
Is MEAN PERFORMANCE OF THE MALE EXERCISE GROUP = MEAN PERFORMANCE OF THE MALE "COUCH
POTATOES"?
and
Is MEAN PERFORMANCE OF THE FEMALE EXERCISE GROUP = MEAN PERFORMANCE OF THE FEMALE
"COUCH
POTATOES"?
or, equivalently,
Is MEAN PERFORMANCE OF THE MALE EXERCISE GROUP - MEAN PERFORMANCE OF THE MALE
"COUCH POTATOES = 0"?
and
Is MEAN PERFORMANCE OF THE FEMALE EXERCISE GROUP - MEAN PERFORMANCE OF THE FEMALE
"COUCH
POTATOES = 0"?
And, further discussion might lead to:
3. If there ARE DIFFERENCES in 2. above:
Is
MEAN PERFORMANCE OF THE MALE EXERCISE GROUP - MEAN PERFORMANCE OF THE MALE
"COUCH POTATOES"
=
MEAN PERFORMANCE OF THE FEMALE EXERCISE GROUP - MEAN PERFORMANCE OF THE FEMALE
"COUCH POTATOES"?
Students can easily discuss these questions without special terminology. Also,
they can discuss "controlling for", "holding fixed" or other expressions that make
sense to them -- WITHOUT SPECIAL TERMINOLOGY.
These TWO-ATTRIBUTE PROBLEMS CAN BE DISCUSSED DURING THE FIRST DAY OF CLASS
TO SHOW THE POWERFUL QUESTIONS THAT CAN BE INVESTIGATED IF THE STUDENTS
STICK WITH THEIR STUDY OF STATISTICS.
Also, it is easy to enter additional predictor attributes if students feel
that such attributes are relevant. Notice that there is no need to discuss
whether or not the FOUR MUTUALLY EXCLUSIVE GROUPS MUST HAVE EQUAL NUMBERS OF
OBSERVATIONS since computers eliminate the computational problems presented
by UNEQUAL N's.
Even if the curriculum does not allow time to actually analyze these questions --
students should be aware of WHAT THEY MIGHT BE ABLE TO DO IF GIVEN THE OPPORTUNITY.
I strongly suggest that students are HIGHLY MOTIVATED by their POWER TO CONTROL FOR
THE
UNCONTROLLABLE. They really like the motto: IF YOU CAN'T CONTROL IT -- MEASURE IT AND
PUT IT IN THE MODEL. In addition, if their future research leads to an interest in the
possible INTERACTION (a special term associated with question #3 above) between
attributes,
then the attributes MUST BE MEASURED AND INCLUDED IN THE MODEL.
And the sermon comes to the end!! Amen!! :-)
-- Joe
*************************************************************
Joe Ward Health Careers High School
167 East Arrowhead Dr 4646 Hamilton Wolfe
San Antonio, TX 78228-2402 San Antonio, TX 78229
Phone: 210-433-6575 Phone: 210-617-5400
Fax: 210-433-2828 Fax: 210-617-5423
[EMAIL PROTECTED]
http://www.ijoa.org/joeward/wardindex.html
*************************************************************
----- Original Message -----
From: SUGHRUE, STEVE <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Thursday, November 18, 1999 7:15 PM
Subject: blocking for variation/confounding
| Hi everyone!
| In the AP course description booklet, multiple choice question
| number 13 asks for the primary reason for blocking when designing an
| experiment. My students and I agree that reducing variation is a good
| answer, but isn't reducing confounding also pretty good? Are we missing
| something here??
| Thanks to anyone who can help .....
|
| Steve Sughrue
| Tabor Academy
| Marion, MA
|
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