[R] reference category in binomal glm

[Marc Schwartz]

On May 27, 2014, at 3:51 AM, Xebar Saram <zeltakc at gmail.com> wrote:

> Hi all
> 
> i know this is probably a silly question but im wondering what is the
> 'reference' category when you run a binomal glm. that is my outcome/DV is
> 0,1 and i run a regression and get coefficients. do the coefficients refer
> to the probability to get 0 or 1?
> 
> thanks so much in advance
> 
> Z


As per the Details section of ?glm:

A typical predictor has the form response ~ terms where response is the (numeric) response vector and terms is a series of terms which specifies a linear predictor for response. 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.


Thus, if you have a numeric 0/1 response, you are predicting 1's and if you use a two level factor, you are predicting the second level of the factor.

Regards,

Marc Schwartz