Compare residuals before and after remediation

Source: R/plotDiagnostics.R · Help: ?plotBeforeAfter

Draws the residuals of two models against their fitted values in two panels, side by side, to show what a remediation method (a weighted fit, a transformation) did to the spread.

Usage

plotBeforeAfter(original, remedied)

Arguments

original

The original lm or glm model.

remedied

The model fitted after remediation.

Value

A ggplot object with one panel per model. Its data have the columns fitted, resid, model ("original" or "remedied") and panel.

Details

A weighted fit is shown through its Pearson residuals \(\sqrt{w_i}\, e_i\), so the plot shows whether the weighting flattened the spread. Its raw residuals would look as heteroscedastic as the original ones however good the weights were.

Each panel has its own axes. Weighted residuals and the residuals of a transformed response are not in the units of the original ones, and on a common axis one of the two panels could be squeezed flat. The panels are there to compare the shape of the two clouds, not their size.

Earlier versions

Up to 0.12.0 the two sets of residuals were overlaid in one panel and told apart by colour.

Examples

data(mtcars)
m1 <- lm(mpg ~ wt, data = mtcars)
m2 <- fitWLS(m1)
plotBeforeAfter(m1, m2)