Average probability of having a dog vaccinated against rabies by charge for vaccination: observed versus owner-stated values for vaccination. The observed values of charges to vaccinate an owned dog against rabies and probability of vaccination came from 3 sources. Points A and B (recording vaccination coverage for all owned dogs vs. costs charged) come from 2 vaccination campaigns held in N'Djaména in 2002 and 2006, respectively. Point C represents the midpoint of the range of recorded 2001 clinic charges in N'Djaména for vaccinating a dog against rabies (costs not adjusted for any potential inflation). The owner-stated amounts that they would be willing to pay for their dogs to be vaccinated against rabies came from a survey of 356 households, conducted in 2006. The graph shows the reverse cumulative probability of the stated values.