Distributions of spectral types for the central concentration in Upper Sco (Figure 5), Taurus (A_J < 1 mag, Esplin & Luhman 2019), IC 348 (A_J < 1.5 mag, Luhman et al. 2016), and the Orion Nebula Cluster (ONC; Da Rio et al. 2012; Hillenbrand et al. 2013). We also show the distribution for Upper Sco after including candidate members that lack confirmation of youth (Table 1). The dashed lines indicate the completeness limits of these samples, and the arrows mark the spectral types that correspond to masses of 0.1 and 1 M_⊙ for ages of a few megayears according to evolutionary models (e.g., Baraffe et al. 1998).