Life is about making difficult decisions in the context of uncertainty, and we hope this model will help you appreciate the trade-offs — and the significance of sustained efforts for social distancing not only by the president but also by each of us in our own lives. Nicholas Kristof ( @NickKristof ) is a columnist for The Times. Stuart A. Thompson ( @stuartathompson ) is a writer and editor for Times Opinion. Methodology Note that this is a model, not the real world; epidemiologists say that in reality the virus without controls would take longer to spread, partly because of growing immunity and partly because people would become much more careful. We are using the S.E.I.R. (Susceptible, Exposed, Infected and Resistant) model; this differs from a model we previously published because it also considers a latency period, when an infected person is not yet contagious. The weather calculation is […]