From: angela baldo <amb82_at_cornell.edu>

Date: Fri 29 Sep 2006 - 22:25:07 GMT

Date: Fri 29 Sep 2006 - 22:25:07 GMT

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-16Received on Sat Sep 30 08:32:57 2006

> 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 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.

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