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tokens: the turbulence-regulated star formation model of Krumholz McKee ( 2005 ) to allow time-variable ff in the prescription of Feldmann Gnedin ( 2011 ), we find that ff ∝ t 2 is most consistent with our data. We conclude that star formation is dynamic on the GMC-scale. 10 10 The time-varying ff may arise from the evolution of star-forming clumps embedded in each GMC. Our study concerns the properties of star formation in clouds that have already formed or in the process of forming stars. By construction, we have limited our analysis to 191 SFC-GMC complexes out of 5469. We found 1014 clouds unmatched to SFCs that have the potential to form star clusters (see Section 6.5 ). We surmise that most (5469-1014-191 = 4264; 78% by number) of the GMCs are gravitationally unbound and will never form massive star clusters. It is possible that some locally dense clumps within an unbound GMC form stars (see e.g., Dobbs et al. 2011 ). These clumps likely give birth to lower mass star clusters that our star formation tracers are not sensitive to. Throughout our analysis, we used free–free emission as a proxy for stellar mass. A more direct measurement would be to count YSOs. For known massive clusters, we find a generally good agreement in the measured stellar mass between free–free emission and YSO counts (see Figure 2 ). A more complete comparison may be possible using all-sky YSO catalogs (e.g., Marton et al. 2016 ). This is an important and natural avenue for future improvement. 8.1. Comments on Stellar Feedback If the rate of star formation in the most massive (10 6 M ⊙ and higher) GMCs does accelerate, the process of star formation must halt before ≳ 0.1, roughly the largest value we see in such clouds. Stellar feedback—in the form of stellar winds, radiation pressure, protostellar jets, and supernovae—from massive star clusters can disrupt the natal cloud and inhibit future star formation. The idea that stellar feedback destroys GMCs was proposed long ago by Larson ( 1981 ). Galactic-scale numerical simulations (e.g., Hopkins et al. 2011 and Faucher-Giguère et al. 2013 ) find that the effects of stellar feedback are necessary for regulating star formation rates to the Kennicutt-Schmidt value. Turbulence in the ISM alone cannot slow the rate of star formation. The existence of large expanding bubbles—a few to ∼100 pc wide—associated with regions bright in free–free emission is evidence for the effects of stellar feedback from young clusters (referred to as SFCs by Rahman Murray 2010 and Lee et al. 2012 ). These massive young clusters, which power most of the free–free emission in the Milky Way, are identified by clear cavities in the 8 μ m emission. The clusters are found in massive GMCs, but the star clusters are not enshrouded in molecular gas—they are instead in regions of ionized gas, which are enshrouded in molecular gas. In some cases, the massive stars may still be accreting gas from their natal protostellar disks, but the disks are not accreting gas