  Many recent works have attempted to constrain the stellar initial mass
function (IMF) inside massive clusters by comparing their dynamical mass
estimates to the measured light. These studies have come to different
conclusions, with some claiming standard Kroupa-type IMFs, while others have
claimed extreme non-standard IMFs. However, the results appear to be correlated
with the age of the clusters, as older clusters (>80 Myr) all appear to be well
fit by a Kroupa-type IMF whereas younger clusters display significant scatter
in their best fitting IMF. Here we show that this is likely due to the fact
that young clusters are out of virial equilibrium and therefore cannot be used
for such studies. Hence only the older clusters are suitable for IMF studies.
Using only these clusters we find that the IMF does not vary significantly. The
youngest clusters can be used instead to constrain the star-formation
efficiency (SFE) within clusters. We find that the SFE varies between 20 and
60% and we conclude that approximately 60% of young clusters are unbound and
will not survive for more than a few 10's of Myr (i.e. "infant mortality").
