[R] R vs. Excel (R-squared)

[Lance Westerhoff]

Hello All-

I found an inconsistency between the R-squared reported in Excel vs.  
that in R, and I am wondering which (if any) may be correct and if  
this is a known issue.  While it certainly wouldn't surprise me if  
Excel is just flat out wrong, I just want to make sure since the R- 
squared reported in R seems surprisingly high.  Please let me know if  
this is the wrong list.  Thanks!

To begin, I have a set of data points in which the y is the  
experimental number and x is the predicted value.  The Excel- 
generated graph (complete with R^2 and trend line) is provided at  
this link if you want to take a look:

http://www.quantumbioinc.com/downloads/public/excel.png

As you can see, the R-squared that is reported by Excel is -0.1005.   
Now when I bring the same data into R, I get an R-square of +0.9331  
(see below).  Being that I am new to R and semi-new to stats, is  
there a difference between "multiple R-squared" and R-squared that  
perhaps I am simply interpreting this wrong, or is this a known  
inconsistency between the two applications?  If so, which is  
correct?  Any insight would be greatly appreciated!


======================

 > # note: a is experimental and c is predicted
 > summary(lm(a~c-1))

Call:
lm(formula = a ~ c - 1)

Residuals:
     Min      1Q  Median      3Q     Max
-2987.6 -1126.6  -181.7   855.3  5602.8

Coefficients:
   Estimate Std. Error t value Pr(>|t|)
c  0.99999    0.01402   71.33   <2e-16 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 1423 on 365 degrees of freedom
Multiple R-Squared: 0.9331,	Adjusted R-squared: 0.9329
F-statistic:  5088 on 1 and 365 DF,  p-value: < 2.2e-16

 > version
          _
platform powerpc-apple-darwin7.9.0
arch     powerpc
os       darwin7.9.0
system   powerpc, darwin7.9.0
status
major    2
minor    2.1
year     2005
month    12
day      20
svn rev  36812
language R

======================


Thank you very much for your time!

-Lance
____________________
Lance M. Westerhoff, Ph.D.
General Manager
QuantumBio Inc.

WWW:    http://www.quantumbioinc.com
Email:    lance at quantumbioinc.com


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