Lead concentrations are sensitive to water composition ) and so it would be expected that there would be some correlation between zones of the same supply. Introducing a different probability for infringing in each supply increases the number of parameters required from one to sixty-three (Model L63 in Table ). With the revised model the two anomalous zones remain anomalous. As a result of introducing 62 additional degrees of freedom 𝜒 2 falls by 164 (from 553 to 389) which when tested against 𝜒 0.01,62 2 (=91) shows that the inclusion of an additional 62 parameters is statistically significant and does account for some of the non-random variation observed. Even when the anomalous zones are removed from the data set the 𝜒 2 associated with the difference between supplies is still statistically significant (compare L-X2 with L63-X2).