Median core size (left panels) and median linewidth, ΔV (right panels) vs. n_eff (at 15 K), shown separately for a sub-sample of proto-stellar (top row) and starless (bottom row) cores. The plot of ΔV vs. n_eff makes use of the single-point observations, instead of spectral line maps as in the left panels, allowing for more molecular lines to be used. The effective densities are listed in Table 2. The plot also includes some detections of the HC₃N(1 − 0) line, with n_eff = 2.5 × 10⁴. The solid line represents the linear fit (from Bayesian statistics) to all points.