UV-to-Hα ratio plotted as a function of age since the onset of star formation for a range of SFHs (single stellar population, single bursts, rising, and constant star formation) computed using the Bruzual & Charlot (2003) models. The shaded band shows the expected ﹩{\mathrm{log}}_{10}[\nu {L}_{\nu }(1500)/{L}_{{\rm{H}}\alpha }]﹩ value for constant star formation, after accounting for a range of metallicities as well as different IMFs. See text for a description of the models.