Dynamical spacing, Δ, between all pairs of adjacent planets in each system in units of mutual Hill radius plotted against their period ratios, P_out/P_in. The figure shows our simulated sample (in magenta) together with the observed sample around MKG dwarfs (in blue). Two important values of dynamical spacing are represented by the dashed lines: the Hill stability criterion (Chambers et al. 1996) in orange and Δ = 10 in gray.