# logistf

## Overview

The package logistf provides a comprehensive tool to facilitate the
application of Firth’s modified score procedure in logistic regression
analysis.

## Installation

```
# Install logistf from CRAN
install.packages("logistf")
# Or the development version from GitHub:
# install.packages("devtools")
devtools::install_github("georgheinze/logistf")
```

## Usage

The call of the main function of the library follows the structure of
the standard functions as lm or glm, requiring a data.frame and a
formula for the model specification. The resulting object belongs to the
new class logistf, which includes penalized maximum likelihood
(‘Firth-Logistic’- or ‘FL’-type) logistic regression parameters,
standard errors, confidence limits, p-values, the value of the maximized
penalized log likelihood, the linear predictors, the number of
iterations needed to arrive at the maximum and much more. Furthermore,
specific methods for the resulting object are supplied. The two
modifications of FL: FLIC and FLAC have been implemented. A function to
generate and plot profiles of the penalized likelihood function and a
function to perform penalized likelihood ratio tests are available.

```
data(sex2)
lf <- logistf(formula = case ~ age + oc + vic + vicl + vis + dia, data = sex2)
summary(lf)
```

## Acknowledgment

This work was supported by the Austrian Science Fund (FWF) (award I
2276).