geweke.plot {coda}R Documentation

Geweke-Brooks plot


If geweke.diag indicates that the first and last part of a sample from a Markov chain are not drawn from the same distribution, it may be useful to discard the first few iterations to see if the rest of the chain has "converged". This plot shows what happens to Geweke's Z-score when successively larger numbers of iterations are discarded from the beginning of the chain. To preserve the asymptotic conditions required for Geweke's diagnostic, the plot never discards more than half the chain.

The first half of the Markov chain is divided into nbins - 1 segments, then Geweke's Z-score is repeatedly calculated. The first Z-score is calculated with all iterations in the chain, the second after discarding the first segment, the third after discarding the first two segments, and so on. The last Z-score is calculated using only the samples in the second half of the chain.


geweke.plot(x, frac1 = 0.1, frac2 = 0.5, nbins = 20,
            pvalue = 0.05, auto.layout = TRUE, ask = TRUE, ...)


x an mcmc object
frac1 fraction to use from beginning of chain.
frac2 fraction to use from end of chain.
nbins Number of segments.
pvalue p-value used to plot confidence limits for the null hypothesis.
auto.layout If TRUE then, set up own layout for plots, otherwise use existing one.
ask Prompt user before displaying each page of plots.
... Graphical parameters.


The graphical implementation of Geweke's diagnostic was suggested by Steve Brooks.

See Also


[Package coda version 0.8-3 Index]