Figure 2.

Statistical signal of the approach to the vaccination thresholds in simulated smallpox elimination. Contagion systems exhibit critical slowing down in the approach to a tipping point such as the vaccination threshold. The coefficient of variation in a moving window provides a measurement of the magnitude of this slowing down. We calculated this statistical signature by first detrending with a one-sided filter and then computing the coefficient of variation in a moving window of 30 observations. This figure shows this statistical signal to begin increasing with the onset of vaccination and to rise dramatically as the approach to the vaccination threshold (vertical dashed line) is approached.