This project is about validation. We would suggest that the best systems for testing the theory of critical slowing down are childhood infections like measles and mumps for which much of the global population is vaccinated. As is well known, some such infections have resurged in recent years, but the time and place at which such re-emergence events occur is seemingly idiosyncratic. In this project, we’re comparing the dynamics of re-emerging childhood infections prior to resurgence events with matched cases where re-emergence didn’t occur. Our goal is to document in this retrospective way if and how soon such re-emergence events might have been anticipated.