Variation in the PL slope α calculated with the shortened duration model given in Eq. (32) as a function of the cloud-scale virial parameter α_vir. Symbol shapes and colors are the same as in Figure 6. The horizontal gray line (band) shows the mean (full spread) of the PL slopes α observed in local clouds (Kainulainen et al. 2014). The reference line given by Eq. (35) with ℛ_α = 0.23 ± 0.06 is shown in black. Combining the systematic variation of dense gas fraction with virial state implied here together with variations in the critical density (depending on α_vir) produces SF efficiencies that match the PHANGS observations in Fig. 1 (see also Fig. C.1 and the discussion in Sect. 6.6).