  Aims. We investigate the validity of the mass segregation indicators commonly
used in analysing young stellar clusters. Methods. We simulate observations by
constructing synthetic seeing-limited images of a 1000 massive clusters (10^4
Msun) with a standard IMF and a King-density distribution function. Results. We
find that commonly used indicators are highly sensitive to sample
incompleteness in observational data and that radial completeness
determinations do not provide satisfactory corrections, rendering the studies
of radial properties highly uncertain. On the other hand, we find that, under
certain conditions, the global completeness can be estimated accurately,
allowing for the correction of the global luminosity and mass functions of the
cluster. Conclusions. We argue that there is currently no observational
evidence of mass segregation in young compact clusters since there is no robust
way to differentiate between true mass segregation and sample incompleteness
effects. Caution should then be exercised when interpreting results from
observations as evidence of mass segregation.
