  Excited nuclear fragments are emitted during nuclear fission. The
de-excitation of these fission fragments takes place as sequential emission of
neutrons followed by photons. A correlation between neutron and photon
multiplicities accompanying fission is thus expected. Fission event generators
based on established statistical nuclear physics models predict a negative
event-by-event correlation in neutron-photon multiplicity. A survey of
published experimental results of an event-by-event covariance between the
neutron and photon multiplicities emitted following the spontaneous fission of
$^{252}$Cf is presented. Analytic unfolding expressions are developed in this
work to determine the bias introduced by background sources, particle
misclassification, pulse pileup, and inelastic photon production. The published
experimental data are re-analyzed using these unfolding techniques and are
found to be in qualitative agreement with the predictions of model-based
calculations. In particular, we have concluded that there exists a significant
event-by-event neutron-photon emission competition following the spontaneous
fission of $^{252}$Cf.
