Figure 7: Childhood Leukemia epidemiology [6]. Map (a): cases (62 circles) are ill children locations; controls (141 crosses) are a sample of the whole population; distances are in km. Cases are significantly clumped, as shown by both functions (b) and (c), drawn as solid lines. shows that in a 0.7 km radius circle around each case, the case density is 70% higher than expected without aggregation ( ). Confidence intervals for the null hypothesis of independence (dotted lines) are computed by Monte-Carlo simulations at the 10% risk level. The poor significance levels are due to too few controls.