Disease clusters in this country are always attributed to some external cause - a nearby chemical plant, power lines or whatever else is in the neighborhood. While these polluters may indeed be causing disease, how much of the cluster phenomenon is due to pure randomness? If the population of the country is infinite (meaning every community has an infinite population), the disease would be spread exactly evenly throughout the population, and there would be no clusters. However, the population is not infinite.

The model below is very simple (believe me, this is not Nobel Prize stuff). A fictional country with a population of 50 million is divided into 10,000 communities, each with a population of 5000. For every single person in every community, the model assigns a random number. For example, if the risk is 1:1000, the model throws out a random number between 1 and 1000 for every one of the 50 million people. If a person gets the unlucky number (I've used the number 13) he has gotten the disease. The total number of affected persons in each community is tallied and the results presented.

Because of the large number of iterations, this takes a few minutes