[R] scatter3d() model.summary coefficients?
angela baldo
amb82 at cornell.edu
Sat Sep 30 00:25:07 CEST 2006
Hello All,
I am a R newbie and am probably misinterpreting something really
obvious...
In the Rcmdr package there is a scatter3d() function that can fit a
curve and also provide coefficients for the model. If I'm understanding
this right, I think it's calling the lower level stats package function
lm(), which is the part that actually does the curve fitting.
Anyway, what has me perplexed is that the model summary from scatter3d()
has different coefficients than the one generated by lm(). However, the
actual surface plotted by scatter3d() looks like the function generated
by lm().
In the scatter3d() docs I didn't see anything about transforming the
coefficients or changing them somehow - perhaps I have not been looking
in the right place?
I'm using a Linux box: 2.6.17-1.2187_FC5smp, R version 2.3.1, Rcmdr
version 1.2-0, in case that helps.
Thanks very much for any enlightenment!
anja
Here's an example of the output on the same data by both functions. If
anyone wants the dataset, let me know:
> scatter3d(samples$x1, samples$y, samples$x2, fit="linear",
residuals=TRUE, bg="white", axis.scales=TRUE, grid=TRUE,
ellipsoid=FALSE, xlab="x1", ylab="y", zlab="x2", model.summary=TRUE)
$linear
Call:
lm(formula = y ~ x + z)
Residuals:
Min 1Q Median 3Q Max
-0.096984 -0.022303 0.004758 0.029354 0.091188
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 0.708945 0.007005 101.20 <2e-16 ***
x 0.278540 0.011262 24.73 <2e-16 ***
z -0.688175 0.011605 -59.30 <2e-16 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 0.03936 on 105 degrees of freedom
Multiple R-Squared: 0.972, Adjusted R-squared: 0.9715
F-statistic: 1822 on 2 and 105 DF, p-value: < 2.2e-16
> summary(lm(formula=samples$y~samples$x1+samples$x2))
Call:
lm(formula = samples$y ~ samples$x1 + samples$x2)
Residuals:
Min 1Q Median 3Q Max
-7865.0 -1808.6 385.8 2380.5 7394.9
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 92204.502 1323.217 69.68 <2e-16 ***
samples$x1 225.882 9.133 24.73 <2e-16 ***
samples$x2 -558.076 9.411 -59.30 <2e-16 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 3192 on 105 degrees of freedom
Multiple R-Squared: 0.972, Adjusted R-squared: 0.9715
F-statistic: 1822 on 2 and 105 DF, p-value: < 2.2e-16
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