There is an interrelationship between four variables. There is a growth forest that has mice, owls and humans. The humans clear the forest for living area and decrease the amount of forest for the animals. When that occurs the mice need space and go into the building the humans built. On the mice is a flea that will cause a deadly virus to the humans. If the population of mice is kept below a certain level no person will get sick (because the mice will live in the forest) but if it goes above a level then people will get ill. The owls are unaffected by the flea. There are 620 acres of forest. Here are the variables: I=number of cases of illness among the villagers M=Mouse population OP=owl population