Histograms of effective radius r_eff (top panel), photometric mass M_phot (middle), and stellar age t (bottom) for young massive bound star clusters (YMCs) in the Milky Way, the Local Group, and in external galaxies. The data are from Table 1. In each panel the clusters from the Milky Way, the Local Group, and external galaxies are cumulatively added to construct three distributions which are shaded differently.