  We present the statistical results of a systematic, unbiased search for
subpulse modulation of 187 pulsars performed with the Westerbork Synthesis
Radio Telescope (WSRT) in the Netherlands at an observing wavelength of 21 cm
(Weltevrede et al. 2006a). We have increased the list of pulsars that show the
drifting subpulse phenomenon by 42, indicating that more than 55% of the
pulsars that show this phenomenon. The large number of new drifters we have
found allows us, for the first time, to do meaningful statistics on the
drifting phenomenon. We find that the drifting phenomenon is correlated with
the pulsar age such that drifting is more likely to occur in older pulsars.
Pulsars that drift more coherently seem to be older and have a lower modulation
index. Contrary claims from older studies, both P_3 (the repetition period of
the drifting subpulse pattern) and the drift direction are found to be
uncorrelated with other pulsar parameters.
