  It is an open question whether glitch activity in individual pulsars varies
on decadal time-scales. The Crab pulsar has experienced 23 spin-up glitches in
the last 36 years, interrupting an otherwise monotonic deceleration. A
homogeneous Poisson process, i.e. a process with constant rate, is not
sufficient to describe the time-ordered distribution of glitch epochs in the
Crab pulsar. There are signs of clustering at the $2\sigma$ level when testing
with Ripley's $K$ function. Two alternative, inhomogeneous models with one and
two step-wise rate changes are found to have higher relative evidence (Bayes
factors of 1.74 and 2.86 respectively) than the homogeneous Poisson process.
The distinction between clustering, where events are correlated, and rate
variation is discussed. The implications for glitch microphysics, in particular
trigger mechanisms based on avalanche processes, are briefly discussed.
