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Re: curve fitting -- Excel Accuracy

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  • Subject: [mg41232] Re: curve fitting -- Excel Accuracy
  • From: "Jerry W. Lewis" <post_a_reply at no_e-mail.com>
  • Date: Thu, 8 May 2003 09:39:58 -0400 (EDT)
  • References: <200304221043.GAA29936@smc.vnet.net> <200304221043.GAA29936@smc.vnet.net> <b8vsbv$dlc$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Your original answer was in response to C B, who asked about curve 
fitting on Excel's chart platform.  Excel's polynomial curve fitting 
from the XY chart platform is actually quite good (better than SAS, 
S-Plus, R, etc).  McCullough, Knusel, etc, provide useful information 
about very real shortcomings in Excel, but they also overlook related 
things that Excel does well.

C B specifically asked about the interpolation routine used by Excel's 
chart smoother:

Excel's chart smoother appears to use Bezier curves.  Brian Murphy has
posted code for Bezier curves.

http://www.xlrotor.com/excel_stuff.htm

In most cases, the difference between Bezier curves and cubic splines is
minimal.  David Braden has posted code for cubic splines

http://groups.google.com/groups?selm=3A11AD33.B1438202%40rochester.rr.com

Jerry

Ian Brooks wrote:

> A number of people wrote and asked for the details of the paper I referred 
> to about Excel's accuracy.
> 
> It is
> 
> "On the Accuracy of Statistical Procedures in Microsoft EXCEL 97" (with 
> Berry Wilson),
> Computational Statistics and Data Analysis 31(1), 27-37, 1999
> 
> 
> There is a new paper that I have not yet read
> 
> "On the Accuracy of Statistical Procedures in Microsoft Excel 2000 and 
> Excel XP" (with Berry Wilson),
> Computational Statistics and Data Analysis 40(4), 713-721, 2002
> 
> 
> I understand there are some differences between the Excel versions, but 
> that the underlying problems have not been addressed and Excel XP is not 
> significantly different than 97.
> 
> Ian
> 
> 
> 
>>>Forget comparisons with Excel.  If you are trying to do anything remotely 
>>>non-trivial Excel is almost certainly giving you garbage.  If you think I 
>>>am exaggerating, take a look at the papers by Bruce McCullough who ran 
>>>the NIST (National Institutes of Standards and Technology) statistics 
>>>benchmark suite through Excel.  The results are appalling, but not 
>>>surprising.  I don't have the paper to hand, but from memory of the 26 
>>>non-linear curve fitting problems posed Excel gave COMPLETELY wrong 
>>>answers to 21 of them!!!  By completely wrong, I mean that where the 
>>>benchmark value is something like 0.6 Excel gave the answer as 13!


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