Virial parameter (α_vir) as a function of clump mass (M_clump) in the left panel, and cloud mass (M) in the right panel. This is shown for the HMSF and non-HMSF sub-samples; these are indicated as red and grey circles, respectively. In the right panel, GMCs with an ATLASGAL match but no HMSF tracer are shown as grey circles with a red outline. The solid horizontal line indicates the critical value of α_vir = 2, for an isothermal sphere in hydrostatic equilibrium without magnetic support. The dashed black line indicates an α_vir = 1. The light grey shading indicates the region where clouds are unstable and likely to be collapsing without additional support from a strong magnetic field. Representative error bars, corresponding to a factor two uncertainty, are shown in the upper-right corner of each panel.