I would suggest running the code:
options('contrasts')
on both machines to see if there is a difference. Having the default
contrasts set differently would be one explanation.
On Tue, Jan 14, 2014 at 2:28 PM, Marc Schwartz <marc_schwa...@me.com> wrote:
>
> On Jan 14, 2014, at 2:23 PM, CASENHISER, DEVIN M <de...@uthsc.edu> wrote:
>
>> 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
>
>
> On my Mac with R 3.0.2, I get the same output as you get on your Windows
> machine.
>
> Something on your Mac is amiss, resulting in the recoding of 'sex' into a
> factor with presumably 0/1 levels rather than the default textual factor
> levels. If you try something like:
>
> model.frame(pitch ~ sex)
>
> the output should give you an indication of the actual data that is being
> used for your model in each case.
>
> Either you have other code on your Mac that you did not include above, which
> is modifying the contents of 'sex', or you have some other behavior going on
> in the default workspace.
>
> I would check for other objects in your current workspace on the Mac, using
> ls() for example, that might be conflicting. If you are running some type of
> GUI on your Mac (eg. the default R.app or perhaps RStudio), try running R
> from a terminal session, using 'R --vanilla' from the command line, to be
> sure that you are not loading a default workspace containing objects that are
> resulting in the altered behavior. Then re-try the example code. If that
> resolves the issue, you may want to delete, or at least rename/move the
> .RData file contained in your default working directory.
>
> Regards,
>
> Marc Schwartz
>
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--
Gregory (Greg) L. Snow Ph.D.
538...@gmail.com
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