  Integrated spectrophotometric properties of stellar systems are intrinsically
dispersed due to the stochastic nature of the small numbers of bright stars
they contain. Among clusters, only the most massive ones can be used
individually for comparison with the mean properties predicted by population
synthesis calculations. The appropriate minimal masses depend, among others, on
the waveband or colour index studied and on age. Selected indices (near-IR CO
and H2O, EW(Halpha)) are used to illustrate the asymmetric nature of the
probability distribution of observable properties and their dependence on
cluster mass.
