One realization of the distribution functions of the lifetimes associated with each protostellar class. The lifetimes are drawn using Eq. (4) with the mean value and standard deviation associated with each lifetime (see text for details). The bin size for each protostellar lifetime distribution is adjusted to the mean value of that distribution, namely the bin sizes are 5×10³ yr, 2.2 × 10⁴ yr, 1.75 × 10⁴ yr, 10⁵ yr, and 2 × 10⁶ yr for the Class 0, Class I, the F Class, Class II, and Class III, respectively.