I've noticed that I get different output when running a linear model on my Mac
versus on my PC. Same effect, but the Mac assumes the predictor as a 0 level
whereas the PC uses the first category (alphabetically).
So for example (using Bodo Winter's example from his online linear models
tutorial):
pitch = c(233,204,242,130,112,142)
sex=c(rep("female",3),rep("male",3))
summary(lm(pitch~sex))
My Mac, running R 3.0.2, outputs:
Residuals:
1 2 3 4 5 6
6.667 -22.333 15.667 2.000 -16.000 14.000
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 177.167 7.201 24.601 1.62e-05 ***
sex1 49.167 7.201 6.827 0.00241 **
---
Signif. codes: 0 *** 0.001 ** 0.01 * 0.05 . 0.1 1
Residual standard error: 17.64 on 4 degrees of freedom
Multiple R-squared: 0.921, Adjusted R-squared: 0.9012
F-statistic: 46.61 on 1 and 4 DF, p-value: 0.002407
But my PC, running R 3.0.2, outputs:
Residuals:
1 2 3 4 5 6
6.667 -22.333 15.667 2.000 -16.000 14.000
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 226.33 10.18 22.224 2.43e-05 ***
sexmale -98.33 14.40 -6.827 0.00241 **
---
Signif. codes: 0 *** 0.001 ** 0.01 * 0.05 . 0.1 1
Residual standard error: 17.64 on 4 degrees of freedom
Multiple R-squared: 0.921, Adjusted R-squared: 0.9012
F-statistic: 46.61 on 1 and 4 DF, p-value: 0.002407
I understand that these are the same (correct) answer, but it does make it a
little more challenging to follow examples (when learning or teaching) given
that the coefficient outputs are calculated differently.
I don't suppose that there is way to easily change either output so that they
correspond (some setting I've overlooked perhaps)?
Thanks and Cheers!
Devin
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