Re: logistic regression having problems with categorical variables

[Werner]

dr soumalya ray <drsoumalya-ray <at> yahoo.co.in> writes:

> 
> hello friends,
> 
> i'd like to point out a problem present in the "logistic regression"
function of PSPP.
> 
> this is a problem stopping usage of PSPP for logistic regression analysis. 
> 
> short description: while doing the logistic regression, pspp completely
ignores "measure" of the
> variable. it is treating categorical variable as a continuous variable
leading to wrong results.
> 
> complete description:
> 1) for reporting this, i am using the example given in this SPSS tutorial- 
> http://www.ats.ucla.edu/stat/spss/dae/logit.htm
> 2) look at the example dataset - binary.sav
> 3) open the file.
> 4) it contains four variables. two nominal (admit and rank) and two scale
(gre and gpa)[visible in the
> "measure" of variable view].
> 5)go to: analyse -> regression-> logistic regression
> 6)select admit as the dependent variable and rank,gre and gpa as the
independent variable. 
> 
> expected result: the output should look like this -
http://i.imgur.com/W5Q4lTI.png
> 
> actual result in pspp: http://i.imgur.com/IEyOUnO.png
> 
> 7) possible reason: pspp ignores the measure indicator of the variable. it
treats rank as a continuous
> variable. 
> 
> 8) this is a long term problem and it exists since the function is
available in pspp. did not report it as was
> unable to confirm the expected result from SPSS. 
> 
> 9) interestingly, if this file is imported in R and logistic regression
analysis done, expected result
> takes place. 
> 
> pspp version: psppire 0.8.5 (problem present since logistic regression
function added in PSPP)
> uname -a:Linux som 4.2.0-21-generic #25~14.04.1-Ubuntu SMP Thu Dec 3
13:55:58 UTC 2015 x86_64 x86_64
> x86_64 GNU/Linux
> 
> regards,
> 
> som
> 

Dear Som,

please try to run the analysis by using the syntax and not from the menu:

logistic regression admit with gre gpa rank 
   /categorical = rank.

Then PSPP should produce the same results as SPSS. I have tried it. 

Hope I could help.

Werner