Dot plots for influence diagnostics

This is a function that can be used to create (modified) dotplots for the diagnostic measures. The plot allows the user to understand the distribution of the diagnostic measure and visually identify unusual cases.

dotplot_diag(
  x,
  cutoff,
  name = c("cooks.distance", "mdffits", "covratio", "covtrace", "rvc", "leverage"),
  data,
  index = NULL,
  modify = FALSE,
  ...
)

Arguments

x	values of the diagnostic of interest
cutoff	value(s) specifying the boundary for unusual values of the diagnostic. The cutoff(s) can either be supplied by the user, or automatically calculated using measures of internal scaling if cutoff = "internal".
name	what diagnostic is being plotted (one of "cooks.distance", "mdffits", "covratio", "covtrace", "rvc", or "leverage"). This is used for the calculation of "internal" cutoffs.
data	data frame to use (optional)
index	optional parameter to specify index (IDs) of x values. If NULL(default), values will be indexed in the order of the vector passed to x.
modify	specifies the geom to be used to produce a space-saving modification: either "dotplot" or "boxplot"
...	other arguments to be passed to ggplot()

Note

The resulting plot uses coord_flip to rotate the plot, so when adding customized axis labels you will need to flip the names between the x and y axes.

Author

Adam Loy loyad01@gmail.com

Examples

data(sleepstudy, package = 'lme4')
fm <- lme4::lmer(Reaction ~ Days + (Days | Subject), sleepstudy)

#Observation level deletion and diagnostics
obs.infl <- hlm_influence(fm, level = 1)

dotplot_diag(x = obs.infl$cooksd, cutoff = "internal", name = "cooks.distance", modify = FALSE)

dotplot_diag(x = obs.infl$mdffits, cutoff = "internal", name = "cooks.distance", modify = FALSE)

# Subject level deletion and diagnostics
subject.infl  <- hlm_influence(fm, level = "Subject")

dotplot_diag(x = subject.infl$cooksd, cutoff = "internal",
             name = "cooks.distance", modify = FALSE)
             
dotplot_diag(x = subject.infl$mdffits, cutoff = "internal", name = "mdffits", modify = "dotplot")