Treatment of Numerical Data - Exp 16

[Robert Zellmer]

I always get a number of questions about Exp 16 and what to do for the
average MW if two of the trials are close and one isn't.  Should you include
all three in the average in this case?

Sometimes the answer is pretty obvious.  If you have 150, 155, 220 hopefully
you realize something is probably wrong with the 220 since the other two are
so close.  I suppose it could happen the 220 is the correct one and somehow
one got two wrong results out of three which were close but this would be
unusual (at least we hope).  In this case the 220 would not be included in
calculating the average MW.  In the discussion section one would list 
all three
MW and the average and explain the one MW was left out of the calculation
of the average (this can be done with the on-line data entry).

Sometimes what to do isn't quite so obvious.  What if the results were 150,
160 and 190.  Should the 190 be included.  If you do, the average rounds to
170 (2 s.f.).  If you don't it rounds to 160 (2 s.f.).  Which is 
correct?  I would
probably go with the 160.  However, to get a correct answer one needs to
do an error analysis and see if the 190 should be included in getting the
average.

I have a link under the "Laboratory" link.  This is a copy of Appendix D
from one of our previous manuals.  Why was it removed for this manual?
I have no idea.  This is courtesy of Dr. Tatz and Dr. Casey.  Here's the 
direct link,

*Treatment of Numerical Data (Error Analysis, sig. fig., graphing)* 
<http://chemistry.osu.edu/%7Erzellmer/chem1220/lab/App_D_122_lab_manual.pdf>

The discussion about how to determine if a data point can be ignored in
such cases is discussed in Section III, "Reporting Results" on pages D-3
through D-5.

By the way, I can't tell you if leaving in one "bad" experimental result 
will lead
to a better or worse average.  That depends on your results and how careful
you were being.  Besides, I don't know what any of the actual true 
results are
for any of the experiments.  Even if I did I couldn't tell you under 
penalty of
death (well maybe not that severe a punishment but close).

Dr. Zellmer
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