[R] zero cells in one variable in logistic regression

Michael Dewey info at aghmed.fsnet.co.uk
Thu Jul 16 11:58:08 CEST 2009


At 10:37 13/07/2009, anna.bucharova wrote:

>Dear all.
>I am sort of beginner with R. I do logistic regression with binomial
>response variable and several continuous and categorical variables. In one
>categorical variable, zero cell occures (2x2 table looks like
>7 - 0
>23 - 25
>This leads to overestimating of odds ratio and inflated confidence interval
>for odds for given variable. The variable is significant in univariate test.
>I do not necessarilly need odd ratio, but I need the explained deviance by
>this variable and I really want to keep this variable in the model. It
>probably matters for explained deviance. How to treat this problem?

Anna, you could consider brglm (from CRAN) which does give you finite 
estimates for the parameter.
@ARTICLE{firth93,
   author = {Firth, D},
   year = 1993,
   title = {Bias reduction of maximum likelihood estimates},
   journal = {Biometrika},
   volume = 80,
   pages = {27--38},
   keywords = {glm}
}
gives the theory

>Thanks for help, Anna Bucharova
>--
>View this message in context: 
>http://www.nabble.com/zero-cells-in-one-variable-in-logistic-regression-tp24458629p24458629.html
>Sent from the R help mailing list archive at Nabble.com.

Michael Dewey
http://www.aghmed.fsnet.co.uk




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