It’s been a while since a user of my plotting-functions asked whether it would be possible to compare multiple (generalized) linear models in one graph (see comment). While it is already possible to compare multiple models as table output, I now managed to build a function that plots several (g)lm-objects in a single ggplot-graph.
The following examples are take from my sjPlot package which is available on CRAN. Once you’ve installed the package, you can run one of the examples provided in the function’s documentation:
# prepare dummy variables for binary logistic regression y1 <- ifelse(swiss$Fertility<median(swiss$Fertility), 0, 1) y2 <- ifelse(swiss$Infant.Mortality<median(swiss$Infant.Mortality), 0, 1) y3 <- ifelse(swiss$Agriculture<median(swiss$Agriculture), 0, 1) # Now fit the models. Note that all models share the same predictors # and only differ in their dependent variable (y1, y2 and y3) fitOR1 <- glm(y1 ~ swiss$Education+swiss$Examination+swiss$Catholic, family=binomial(link="logit")) fitOR2 <- glm(y2 ~ swiss$Education+swiss$Examination+swiss$Catholic, family=binomial(link="logit")) fitOR3 <- glm(y3 ~ swiss$Education+swiss$Examination+swiss$Catholic, family=binomial(link="logit")) # plot multiple models sjp.glmm(fitOR1, fitOR2, fitOR3)
Thanks to the help of a stackoverflow user, I now know that the order of aes-parameters matters in case you have dodged positioning of geoms on a discrete scale. An example: I use following code in my function
ggplot(finalodds, aes(y=OR, x=xpos, colour=grp, alpha=pa)) to apply different colours to each model and setting an alpha-level for geoms depending on the p-level. If the alpha-aes would appear before the colour-aes, the order of lines representing a model may be different for different x-values (see stackoverflow example).