[R] factor variables in logistic regression

[Kevin E. Thorpe]

On 05/11/2016 08:00 AM, ch.elahe via R-help wrote:
> Hi all,
>
> I have a plot for TSTMean vs. SNRMean and both of these variables are factors. How can I use Logistic Regression for factor variables?
> Currently I use model=lm(TSTMean~SNRMean,data=df) but when I check summary(model) I get this error: r error in quartile.default (resid) factors are not allowed
>
> thanks for any help,
> Elahe
>

First of all, lm() is for linear regression, not logistic regression. 
For logistic regression you need to use glm() and make sure you set the 
correct family (see ?glm). I don't recall if glm() accepts a factor 
outcome but if not, you would need to re-code it to 0/1.

Kevin

-- 
Kevin E. Thorpe
Head of Biostatistics,  Applied Health Research Centre (AHRC)
Li Ka Shing Knowledge Institute of St. Michael's Hospital
Assistant Professor, Dalla Lana School of Public Health
University of Toronto
email: kevin.thorpe at utoronto.ca  Tel: 416.864.5776  Fax: 416.864.3016