  A fundamental property determining the transient behaviour of core-collapse
supernovae (CCSNe) is the amount of radioactive $^{56}$Ni synthesised in the
explosion. Using established methods, this is a relatively easy parameter to
extract from observations. Here I provide a meta analysis of all published
$^{56}$Ni masses for CCSNe. Collating a total of 258 literature $^{56}$Ni
masses I compare distributions of the main CCSN types: SNeII; SNeIIb; SNeIb;
SNeIc; and SNeIcBL. Using these published values, I calculate a median
$^{56}$Ni mass of 0.032${\rm\ M}_\odot$ for SNeII (N=115), 0.102${\rm\
M}_\odot$ (N=27) for SNeIIb, SNeIb = 0.163${\rm\ M}_\odot$ (N=33), SNeIc =
0.155${\rm\ M}_\odot$ (N=48), and SNeIcBL = 0.369${\rm\ M}_\odot$ (N=32). On
average, stripped-enevelope SNe (SE-SNe: IIb; Ib; Ic; and Ic-BL) have much
higher values than SNeII. These observed distributions are compared to those
predicted from neutrino-driven explosion models. While the SNII distribution
follows model predictions, the SE-SNe have a significant fraction of events
with $^{56}$Ni masses much higher than predicted. If the majority of published
$^{56}$Ni masses are to be believed, these results imply significant
differences in the progenitor structures and/or explosion properties between
SNeII and SE-SNe. However, such distinct progenitor and explosion properties
are not currently favoured in the literature. Alternatively, the popular
methods used to estimate $^{56}$Ni masses for SE-SNe may not be accurate.
Possible issues with these methods are discussed, as are the implications of
true $^{56}$Ni mass differences on progenitor properties of different CCSNe.
