Date:         Tue, 2 Sep 2008 21:05:23 -0400
Reply-To:     Peter Flom <peterflomconsulting@mindspring.com>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Peter Flom <peterflomconsulting@MINDSPRING.COM>
Subject:      Re: Class variables proc logistic
Comments: To: tal <talila.ar@GMAIL.COM>
Content-Type: text/plain; charset=UTF-8

 tal <talila.ar@GMAIL.COM> wrote
>I'm not sure- but i don't think the sampling is stratified. i have ,
>lets say:20 variables- "is XX important to you?" for each quest the
>response is
>1- important 2- not important 3-no answer.
>(When i use the class statement- 3 dummy variables are created, but
>I'm only interested in the first two- the third one is created
>automatically- but i don't need it- and that's where I have a
>problem)   As i said , for each observation i want to count the number
>of missing values in the questionnaire- and take it as explanatory
>variable- but since a dummy variable is created for each var1-var20
>the number of missing values is a linear combination of these.
> Does anybody know how to create only the 2 dummy variables that i
>need in proc logistic, and drop the third one?
>

If your IV has 3 levels, then LOGISTIC will create 2 dummy variables;, by default SAS uses EFFECT coding, and dummy (or reference) coding, is often better, but I don't think that explains your problem


So, could you show your code?

e.g

data today;
 length IV $4;
 input iv $ dv $ weight;
 datalines;;
 Imp yes 100
 NotI yes 200
 NA  yes 50
 Imp no 50
 NotI no 100
 NA  no  50
;;;;

proc logistic data = today;
 class iv (param = ref);
 model dv = iv;
 weight weight;
run;

creates two dummy variables

Peter

Peter L. Flom, PhD
Statistical Consultant
www DOT peterflom DOT com