Ensemble SF as a function of Δt (a) and Δt/τ (b) at different wavelengths for each group, color-coded by the average bolometric luminosity. Different symbols indicate the different wavelengths used for continuum extraction. Panel (b) assumes that the SFs all follow a single universal function if Δt is converted to units of τ ∝ L_bol^aλ_RF^b. Note that the values of Δt/τ on the x-axis are only meaningful in relative terms. The solid black line represents the best-fit universal SF.