Correlation plot of the logarithm of the virial parameter and the logarithm of the gas mass as black points for masses calculated using the NH₃ line width, as red points using the N₂H⁺ line width, and as green points for the C¹⁷O line width. The horizontal black line indicates a virial parameter of 1. A fit to each data set is shown as straight lines. The upper panel illustrates the contour plot, for which we counted the number of sources in each logarithmic gas mass and virial parameter bin of 0.3 in black for masses computed from the NH₃ line width and in red for the N₂H⁺ line width.