Predictors selected by five-fold cross validation and forward selection.

The top four variables were selected in the identical order (as listed) across all surveillance threshold models. The fifth predictor, relative variance in transmissibility, was included in all models, but not always as the fifth chosen. In the formulas, c refers to cluster-level quantities. The rightmost column gives the full range of fitted coefficients (log-odds) across all models based on the five-fold cross validation for each surveillance thresholds’ final model. *var(σc) was calculated across all hosts; var(Seff) was calculated across only infected hosts. I = number of infected hosts, N = total number of hosts, σc = effective susceptibility to infection by cluster c, βk = the transmission rate of the virus carrying k deleterious mutations. Formulas to calculate each quantity are in S1 Table.