rrocproc-r-package

Changing scale of the ROC chart

I am using the following code to plot the ROC curve after having run the logistic regression. 

fit1 <- glm(formula=GB160M3~Behvscore, data=eflscr,family="binomial", na.action = na.exclude)
prob1=predict(fit1, type=c("response"))
eflscr$prob1 = prob1

library(pROC)
g1 <- roc(GB160M3~prob1, data=eflscr, plot=TRUE,  grid=TRUE, print.auc=TRUE)

The ROC curves plotted look like this (see link below)

enter image description here

  1. The x-axis scale does not fill the who chart.
  2. How can I change the x axis to report 1 - specifically?
Solution

    1. By default pROC sets asp = 1 to ensure the plot is square and both sensitivity and specificity are on the same scale. You can set it to NA or NULL to free the axis and fill the chart, but your ROC curve will be misshaped.

      plot(g1, asp = NA)

      Using par(pty="s") as suggested by Joe is probably a better approach

    2. This is purely a labeling problem: note that the x axis goes decreasing from 1 to 0, which is exactly the same as plotting 1-specificity on an increasing axis. You can set the legacy.axes argument to TRUE to change the behavior if the default one bothers you.

      plot(g1, legacy.axes = TRUE)