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

tal <> 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?


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

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