R help - Sep 2011 - logistic regression: default computed probability

Hello all,

Suppose in a logistic regression model, the binary outcome is coded as
0 or 1.
In SAS, the default probability computed is for Y = 0 (smaller of the
two values) . However, in SPSS the probability computed is for Y = 1
(greater of the two values).

Which one does R compute, the probability for the smaller or the
greater value?

I went through the documentation in a hurry but couldn't find a clue.

Thanks

Nikhil

On Sep 21, 2011, at 10:25 AM, n wrote:
> Hello all,
> 
> Suppose in a logistic regression model, the binary outcome is coded as
> 0 or 1.
> In SAS, the default probability computed is for Y = 0 (smaller of the
> two values) . However, in SPSS the probability computed is for Y = 1
> (greater of the two values).
> 
> Which one does R compute, the probability for the smaller or the
> greater value?
> 
> I went through the documentation in a hurry but couldn't find a clue.
> 
> Thanks
> 
> Nikhil
>From ?glm in the Details section:
For binomial and quasibinomial families the response can also be specified as a
factor (when the first level denotes failure and all others success) or as a
two-column matrix with the columns giving the numbers of successes and failures.

So P(Y = 1) if using 0/1.

HTH,

Marc Schwartz