Re: precision/accuracy

[Tom Ford <tomford@THESCIENCESOURCE.COM>]

At 07:55 PM 8/31/99 -0400, Michael D. Edmiston, Ph.D. wrote:

> Ken Fox asked what we think of the target practice example for
> precision and accuracy.  I think it is a frequently cited example, and
> I think it is a good one.  The typically student ought to be able to
> have a pretty clear visual image of this... and it's even pretty easy
> to draw on the board.

It is even easier and more memorable to DO IT ON THE BOARD, as some persons
on this list have seen me demonstrate:

Draw a "target" on the chalkboard. Stand at the back of the room or top
deck of the lecture room with your hunting slingshot and three pieces of
chalk. It is easy to become the marksman with a little practice so that you
can place the first shot high, the second low to the left, and the third
one low to the right. Then come down to the board again and treat the three
data as a center of mass problem. Students will follow your finding and
marking the centroid as the "average", and behold, it is a heart shot! Your
weapon is accurate, but it will not put supper on the table! Then fire
three more pieces of chalk in a cluster smaller than your fist, but in the
outer ring. Now your weapon is more precise, but not very accurate. It is
easy to see this more precise tool can be made more acurate by aiming
better. The distance between the centroid of three shots and the most
extreme of those shots pictures the precision. the distance between the
centroid of three shots and the center of the bullseye pictures the
accuracy. From there, one can use heavier language appropriate for the
audience to deal with error, uncertainty, &c -- even resolution.

To follow on, this is also a good time to challenge some particular student
to a chalk fight. There is something highly intuitive about slingshots and
both the student and the instructor will do well. Yes, you can do this with
hundreds in the room, but maybe not from the VERY back. Then just be
careful where you store the slingshot.

> Ken also asked if this example has anything analogous to resolution.
> Mark Sylvester asked if the bullet hole size might serve this purpose.
> I would agree with Mark.  I think resolution in this example would be
> how well we can tell where each "bullet" went.  I put bullet in
> quotations because the worst case scenario would be a shotgun... unless
> we allow exploding bullets.

Even the "worst case" can be tamed by finding the centroid.

> Michael D. Edmiston, Ph.D.              Phone/voice-mail:       419-358-3270
> Professor of Chemistry & Physics        FAX:                    419-358-3323
> Chairman, Science Department            E-Mail
edmiston@bluffton.edu
> Bluffton College
> 280 West College Avenue
> Bluffton, OH 45817
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