R help - Jul 2011 - Different result of multiple regression in R and SPSS

Hi, I am trying to do a simple multiple regression analysis that has one
nominal variable (gender) and three numeric variables as independent
variables and one numeric variable as dependent variable.

So, I got a formula like this:
summary(out.3 <- lm(scale(DV) ~  gender + scale(IV.1) + scale(IV.2) +
scale(IV.3))

I tried to compare the outcome in R with the outcome in SPSS and found the
results are different!
I found that R and SPSS have the exact same outcome when every variable is
numeric; however, whenever I included "gender (0/1)" variable in the
equation, the result become different.

I guess that SPSS automatically treat gender as a numeric variable and
standardize it when running analysis. So, I tried to change "gender"
to a
numeric variable and ran analysis but the results were still not identical.

What is the problem here and what is the right way to do this analysis?
Thanks,

Jay Yang

--
View this message in context:
http://r.789695.n4.nabble.com/Different-result-of-multiple-regression-in-R-and-SPSS-tp3679423p3679423.html
Sent from the R help mailing list archive at Nabble.com.

Answer: Contrasts, i.e. the parameterization of the categorical variable(s) df.

?contrasts may be of some help, but you really need to do some
background studying of the linear models principles involved. Googling
may provide tutorials. Also searching the mail archives, e.g.:

https://stat.ethz.ch/pipermail/r-help/2009-February/187479.html

-- Bert

On Tue, Jul 19, 2011 at 2:39 PM, J. <seoulseoulseoul at gmail.com>
wrote:
> Hi, I am trying to do a simple multiple regression analysis that has one
> nominal variable (gender) and three numeric variables as independent
> variables and one numeric variable as dependent variable.
>
> So, I got a formula like this:
> summary(out.3 <- lm(scale(DV) ~ ?gender + scale(IV.1) + scale(IV.2) +
> scale(IV.3))
>
> I tried to compare the outcome in R with the outcome in SPSS and found the
> results are different!
> I found that R and SPSS have the exact same outcome when every variable is
> numeric; however, whenever I included "gender (0/1)" variable in
the
> equation, the result become different.
>
> I guess that SPSS automatically treat gender as a numeric variable and
> standardize it when running analysis. So, I tried to change
"gender" to a
> numeric variable and ran analysis but the results were still not identical.
>
> What is the problem here and what is the right way to do this analysis?
> Thanks,
>
> Jay Yang
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Different-result-of-multiple-regression-in-R-and-SPSS-tp3679423p3679423.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org 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.
>


-- 
"Men by nature long to get on to the ultimate truths, and will often
be impatient with elementary studies or fight shy of them. If it were
possible to reach the ultimate truths without the elementary studies
usually prefixed to them, these would not be preparatory studies but
superfluous diversions."

-- Maimonides (1135-1204)

Bert Gunter
Genentech Nonclinical Biostatistics

Thanks for the answer.

However, I am still curious about which result I should use? The result from
R or the one from SPSS?
Why the results from two programs are different?

Jay

--
View this message in context:
http://r.789695.n4.nabble.com/Different-result-of-multiple-regression-in-R-and-SPSS-tp3679423p3679511.html
Sent from the R help mailing list archive at Nabble.com.

On Jul 19, 2011, at 6:29 PM, J. wrote:
> Thanks for the answer.
>
> However, I am still curious about which result I should use? The  
> result from
> R or the one from SPSS?
It is becoming apparent that you do not know how to use the results  
from either system. The progress of science would be safer if you get  
some advice from a person that knows what they are doing.
> Why the results from two programs are different?
Different parametrizations. If I had to guess I would bet that the  
gender coefficient is R is exactly twice that of the one from SPSS.  
They are probably both correct in the context of their respective  
codings.

-- 
David Winsemius, MD
West Hartford, CT

On Tue, Jul 19, 2011 at 3:45 PM, David Winsemius <dwinsemius at
comcast.net> wrote:
>
> On Jul 19, 2011, at 6:29 PM, J. wrote:
>
>> Thanks for the answer.
>>
#########################
>> However, I am still curious about which result I should use? The result
>> from
>> R or the one from SPSS?
>
> It is becoming apparent that you do not know how to use the results from
> either system. The progress of science would be safer if you get some
advice
> from a person that knows what they are doing.
##########################
I nominate this for an R fortune.

-- Bert
>
>> Why the results from two programs are different?
>
> Different parametrizations. If I had to guess I would bet that the gender
> coefficient is R is exactly twice that of the one from SPSS. They are
> probably both correct in the context of their respective codings.
>
> --
> David Winsemius, MD
> West Hartford, CT
>
> ______________________________________________
> R-help at r-project.org 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.
>

@Dimitri: I tried to enter it as numeric and still got the same outcome. I
still wonder if there is any way to get the same result from both programs.
@David, Bert: Yes, I found that the gender coefficient is R is exactly twice
that of the one from SPSS. Need to study on parametrization.
Thanks,

Jay

--
View this message in context:
http://r.789695.n4.nabble.com/Different-result-of-multiple-regression-in-R-and-SPSS-tp3679423p3679590.html
Sent from the R help mailing list archive at Nabble.com.

On Tue, Jul 19, 2011 at 4:19 PM, J. <seoulseoulseoul at gmail.com>
wrote:
> @Dimitri: I tried to enter it as numeric and still got the same outcome. I
> still wonder if there is any way to get the same result from both programs.
There is. ?C ?contrasts

But of course you must do your homework to understand how to use
these. (See the quote in my signature).

-- Bert



> @David, Bert: Yes, I found that the gender coefficient is R is exactly
twice
> that of the one from SPSS. Need to study on parametrization.
> Thanks,
>
> Jay
>
 PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
"Men by nature long to get on to the ultimate truths, and will often
be impatient with elementary studies or fight shy of them. If it were
possible to reach the ultimate truths without the elementary studies
usually prefixed to them, these would not be preparatory studies but
superfluous diversions."

-- Maimonides (1135-1204)

Bert Gunter
Genentech Nonclinical Biostatistics
467-7374
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm