We have sought correlations between the fraction of null pulses with other pulsar parameters for an ensemble of 72 pulsars using survival analysis methods. The strongest correlation was found between the null fraction and pulse period. Correlations were also found between other parameters that typically have strong dependencies on pulse period, and this tends to indicate that the null fraction increases with age as was first suggested by Ritchings (1976). However, no explicit correlation was found between pulsar characteristic age and null fraction. A significant anti-correlation was found between the angle subtended by the magnetic and rotation axes and the null fraction.
Many of the pulsars presented here were found to null. In particular, all pulse profile classes in the scheme devised by Rankin (1983a) have members that null. Differences in the mean age of these pulsar classes are not very pronounced, and the influence of class on pulse nulling statistics is probably less than that suggested by Rankin (1986), but cannot entirely be ruled out. Also, there is considerable variation in the fraction of null pulses from pulsars within each class, but generally class St pulsars null the least. Of special note is the fact that two pulsars PSR 0833-45 and PSR 1556-44 apparently do not null. The upper limit for PSR 0833–45 is quite low; no nulls were detected in observations of over 120,000 pulses.
The similarity of the nulling parameters of pulsars observed at two frequencies near 400 MHz and 843 MHz suggests that the pulsar emission mechanism is wide band over this frequency range.