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st: RE: -logit- interpretation question


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: -logit- interpretation question
Date   Fri, 27 Nov 2009 20:04:36 +0100

<>

The only useful variation in y is whenever x1 equals 3. Whenever it is 2 or
1, y==0, whenever it is bigger than 3, y==1. To see that, look at the obs
that -logit- used:

*******
su y x1 if e(sample)
*******


Note the manual deals with this issue: [R], p. 906-910

HTH
Martin


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Michael Crain
Sent: Freitag, 27. November 2009 19:59
To: Statalist
Subject: st: -logit- interpretation question

I have a data set of 35 observations with the predictor variable (x1) using
the Likert scale and y = 0 or 1. 
I run -logit- and -logistic- (Stata v 10) and get a result that says:
 
note: outcome = x1> 3 predicts data perfectly except for
      x1 == 3 subsample:
      x1 dropped and 28 obs not used
 
-logit- is dropping 28 of the 35 observations and is using only 7
observations 
for the logit model but I don't understand the theoretical reason for doing
so. 
 
 
clear
input y x1
1 4
1 4
1 3
1 4
1 4
1 4
1 4
1 3
1 3
1 3
1 3
0 3
0 1
0 2
0 2
0 2
0 2
0 2
0 2
0 2
0 2
0 2
0 2
0 3
0 2
0 1
0 1
0 2
0 1
0 2
0 1
0 2
0 1
0 1
0 1
end
scatter  y x1, jitter(5)
tab y x1
logit y x1
logistic y x1

 		 	   		  
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