[R] Odd r-squared
Simon Wotherspoon
Simon.Wotherspoon at utas.edu.au
Mon Nov 3 07:53:25 CET 2003
Hi,
I would consider the calculation of r-squared in the following to be a
bug, but then, I've been wrong before. It seems that R looks to see if the
model contains an intercept term, and if it does not, computes r-squared in
a way I don't understand. To my mind, the following are two alternative
parametrizations of the same model, and should yield the same r-squared.
Any insight much appreciated
Simon.
> set.seed(10,kind=NULL)
> x <- runif(10)
> g <- gl(2,5)
> y <- runif(10)
>
> summary(lm(y ~ g*x))
Call:
lm(formula = y ~ g * x)
Residuals:
Min 1Q Median 3Q Max
-0.35205 -0.14021 0.02486 0.13958 0.39671
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 0.3138 0.2749 1.141 0.297
g2 -0.1568 0.4339 -0.361 0.730
x 0.3556 0.6082 0.585 0.580
g2:x 0.3018 1.0522 0.287 0.784
Residual standard error: 0.276 on 6 degrees of freedom
Multiple R-Squared: 0.1491, Adjusted R-squared: -0.2763
F-statistic: 0.3505 on 3 and 6 DF, p-value: 0.7907
> summary(lm(y ~ g/x-1))
Call:
lm(formula = y ~ g/x - 1)
Residuals:
Min 1Q Median 3Q Max
-0.35205 -0.14021 0.02486 0.13958 0.39671
Coefficients:
Estimate Std. Error t value Pr(>|t|)
g1 0.3138 0.2749 1.141 0.297
g2 0.1570 0.3357 0.468 0.657
g1:x 0.3556 0.6082 0.585 0.580
g2:x 0.6574 0.8586 0.766 0.473
Residual standard error: 0.276 on 6 degrees of freedom
Multiple R-Squared: 0.8061, Adjusted R-squared: 0.6769
F-statistic: 6.237 on 4 and 6 DF, p-value: 0.02491
--please do not edit the information below--
Version:
platform = i386-pc-mingw32
arch = i386
os = mingw32
system = i386, mingw32
status =
major = 1
minor = 8.0
year = 2003
month = 10
day = 08
language = R
Windows ME 4.90 (build 3000)
Search Path:
.GlobalEnv, package:methods, package:ctest, package:mva, package:modreg,
package:nls, package:ts, Autoloads, package:base
---
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