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-----Original Message-----important
From: Forum for Physics Educators [mailto:PHYS-
L@list1.ucc.nau.edu] On Behalf Of John Denker
Sent: Wednesday, October 05, 2005 2:36 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Charts or Graphs, and other Excel stuff
Edmiston, Mike wrote in part:
(3) Suppose the intercept of a linear regression is an
regression lineparameter for the report. Excel automatically runs the
extend thefrom the first data point to the last data point. It doesn't
manuallyregression line to visually show the intercept unless you
even after Iextend it. I expect students to do this, but many don't,
somethingtell them.
At the risk of ruining my reputation by actually knowing
about windows and even saying something not-totally-nasty aboutit,
I don't see what the problem is here.function
Excel has a usable (not very good, but usable) worksheet
called LINEST. It will fit a straight line (y = m x + b) toyour data,
and return you m, b, and a bunch of additional statistics,including
the standard error of m and the standard error on b.parameter,
1) Since we are supposing that the intercept is an important
everybody should be using LINEST to calculate this parameter!the
Also it wouldn't kill them to calculate the standard error on
intercept, either.are
2) Having calculated m and b, it is straightforward to draw the
fitted line, extended however you please.
3) Yes, I am aware that y = m x + b is not necessarily the most
numerically-stable representation for a straight line. There
tricks you can do to improve the stability of LINEST, but the"automatic"
details are beyond the scope of this note.
========
Just because the prog has an automatic feature doesn't mean you
are obliged to use it. I didn't even know there was an
regression line feature. I don't plan to pollute my brain byto
learning how to use it.
It may be that LINEST is a not-quite standard feature that has
be loaded from some library. I wouldn't know such details.But
if so, anybody enrolled in physics should have long-sinceloaded
whatever libraries are needed for stuff like this.entering
========
LINEST is an "array function". Be sure you know the trick for
an array function. (Mostly: control-shift-enter.)