Ripley's L function for an particular epidemic. These three examples show variability and characteristics of the spatial clustering. Plotted in dark gray, the Ripley's L function for the observed data against distance. The Ripley's L function for observed data (dark gray) is plotted bold when statistically significant (i.e., outside the bootstrapping envelop), but otherwise is dashed. The light gray area was defined by the 10000 bootstrapping replications, these replications were constructed using all the cases for a particular epidemic. The most significant cluster size, or simply cluster size, is defined as the distance at which the difference between the bootstrapping envelope and the observation is maximum (black bold vertical segment), this is indicated by the vertical dashed line in the figure. The top panel shows a case where the cluster size is relatively large (2340 meters) but small scale significant clusters are also present. The bottom-left shows a cluster size with small scale (50 meters) without the occurrence of clusters at large scales. The bottom-right displays a large cluster size (5010 meters) without clusters at small scales.