Test of coeval population. Top: The open histogram represents the age distribution simulated for a sample of stars uniformly distributed along a 2.2 Myr isochrone from Siess et al. (2000), assuming an observational uncertainty in the luminosity of σ(log L) = 0.10. The spread in age is σ(log t) = 0.13. The hatched histogram shows the observed age distribution for the observed completeness-limited subsample. Bottom: Cumulative functions of the the two distributions. Solid and dotted line represent the observed and simulated sample, respectively.