
124 Statistical Computing in Nuclear Imaging
One approach that should always be used for testing for the conver
gence
to the equilibrium is to lo ok at the Markov trace which is a plot of some QoI
vs. the number of Markov step as illustrated in Figure 4.10. The trace shows
the evidence of poor mixing and can also provide an estimate of the burn-in
period. It must be cautioned however that the actual burn-in time c an be
much longer than sugg ested by the trace, but it is often obvious based o n the
trace that the burn-in is incomplete.
A more formal test for re aching the equilibrium is also available. For ex-
ample, suppose we determined the po int