# Plotting a logistic GAM model in R - why is the scale not 0-1?

I have fit a simple binary logistic GAM model in R and have used the plot() function to plot the results of this model. The outputted graph shows a fitted line and a confidence interval, but the scale is clearly not 0-1. Does anyone know what is being plotted? Ideally I would like to get a graph of the predicted probability of the outcome versus the continuous predictor. Does anyone know how to get that out?

Thanks

• You should post this on stackoverflow.com – danas.zuokas Jun 21 '12 at 10:18
• Add some sample code to this question. Specify what packages you are using. There are multiple packages that allow GAM modelling in R. – John Jun 21 '12 at 11:13
• perhaps the log odds is being plotted. – Macro Jun 21 '12 at 21:37

The individual plots are on the scale of the linear predictor, i.e. a scale that is -Inf to +Inf. The inverse of the link function is used to map from this scale to the 0, ..., 1 scale of the response. Further note that each smooth is subject to centring constraints and so is centred about 0.
• The predict function often has a variable type and for a logistic regression you could use type="response". – Wayne Jun 21 '12 at 12:42