Figure 3

The degree structure of the unit network. Panel A shows the probability density function of the in-degree - the number of units from which a unit has received patients. The curve is a fit to a power-law times an exponential function - a typical functional shape for skewed distributions where there is a natural maximum (in this case the total number of units). The mathematical expression of the curve is $a_{1}exp(-k_{\mathrm{in}}/a_2)k_{\mathrm{in}}^{-a_3}$ with $a_1=0.15\pm 0.01$, $a_2=760\pm 16$ and $a_3=0.44\pm 0.01$. Panel B shows that the in- and out-degrees are strongly correlated but there is weak tendency for large-degree nodes to have larger in- than out degrees. The background scatter plot shows values for individual units. The hollow circles are average values over bins. The bars indicate the standard errors of these points.