The backdating exercise for Lombardy

Accounting for event sequence: the 1|1|1 rule and the backdating exercise

The backdating exercise is a simple way to correct new cases curves for the sequence of events they reflect: a ”case” is typically the report of a diagnostic test indicating the patient is infected. But the epidemiologically important event is the contagion event: the moment the patient contracted the virus, which is normally unobserved. To find out when the contagion event happened we have to backdate from the reported test to the contagion event. The 1|1|1 rule and the backdating exercise give us a quick way to do this.

In a dynamic environment, we are watching echoes of past events, and it is important to shift these events back in time to avoid oversteering after the fact. Belated oversteering is the #2 reason why dynamic systems with information cascades become volatile and eventually collapse.

1|1|1: the simple version

This is the 1|1|1 rule.

Examples of backdating exercises

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