MPDiR (version 0.1-15)

binom.diagnostics: Diagnostics for Binary GLM

Description

Two techniques for evaluating the adequacy of the binary glm model used in mlds, based on code in Wood (2006).

Usage

binom.diagnostics(obj, nsim = 200, type = "deviance", no.warn = TRUE)
## S3 method for class 'binom.diag':
plot(x, alpha = 0.025, breaks = "Sturges", ...)

Arguments

obj

Object of class glm from a fit to data with a binary response.

nsim

number of bootstrap simulations to run.

type

character indicating type of residuals (defaults to deviance) to use in the simulations.

no.warn

logical indicating whether to suppress warnings from glm. Defaults to TRUE.

x

object of class binom.diag, typically obtained from running binom.diagnostics

alpha

confidence level for envelope of the distribution of residuals

breaks

character indicating algorithm for choosing the breaks in the histogram of runs of residuals. Defaults to Sturges. See hist.

...

additional parameters specifications for the empirical cdf plot

Value

• binom.diagnostics returns a list of class binom.diag with components
• NumRuns
  integer vector giving the number of runs obtained for each simulation
• resid
  numeric matrix giving the sorted deviance residuals in each column from each simulation
• Obs.resid
  numeric vector of the sorted observed deviance residuals
• ObsRuns
  integer giving the observed number of runs in the sorted deviance residuals
• p
  numeric giving the proportion of runs in the simulation less than the observed value.

Details

Wood (2006) describes two diagnostics of the adequacy of a binary glm model based on analyses of residuals (see, p. 115, Exercise 2 and his solution on pp 346-347). The first one compares the empirical cdf of the deviance residuals to a bootstrapped confidence envelope of the curve. The second examines the number of runs in the sorted residuals with those expected on the basis of independence in the residuals, again using a resampling based on the models fitted values. The plot method generates two graphs, the first being the empirical cdf and the envelope. The second is a histogram of the number of runs from the bootstrap procedure with the observed number indicated by a vertical line. Currently, this only works if the glm method is used to perform the fit and not the optim method

References

Wood, SN Generalized Additive Models: An Introduction with R, Chapman & Hall/CRC, 2006.

Examples

# generate psychometric function and binary data
levs <-  10^seq(-2, 0, len = 5)
psyF <-  pnorm(levs, mean = 0.2, sd = 0.2)
Ntrials <- 100
Resp <- rbinom(Ntrials * length(psyF), 1, psyF)
d.df <- data.frame(resp = Resp, levs = levs)
fit.glm <-  glm(resp ~ levs, binomial, d.df)
fit.diag <- binom.diagnostics(fit.glm)
plot(fit.diag)