Fig. 2.

CCM skill (ρ) as a function of cross-map lag (negative values indicate that causes precede effects). (A) The susceptible–infected–recovered–susceptible (SIRS) model with synchrony between flu and a periodic driver shows no well-defined optimal lag. (B) An empirical example showing the same pattern. Note that selecting the lag with the maximum CCM value over the window used in ref. 1 (dashed lines) obscures the fact that the optimal lag is not unique and thus has little information about the direction of causation.