Incident Impact Calculation Formula

The Mike Nakis formula for calculating the impact of an incident:

I = S × G × T

Where:

• I is the impact of the incident.
• S is the severity of the incident.
• G is the geographic pervasiveness of the incident.
• T is the temporal pervasiveness of the incident.
  

Thus:

• An incident of high severity does not have high impact if it happens rarely and in only a few places.
  
• An incident of low severity can have high impact if it is persistent and widespread.

For example: 

The sinking of the Titanic was certainly a disaster, but it was largely an isolated incident: it happened only once, on the 15th of April 1912, and only in one place, at 41°43′32″N 49°56′49″W; we have not had anything quite like that happening before, and we have been doing a decent job at avoiding similar incidents ever since, so in the big picture, it is not of particularly high impact.

On the other hand:

A modern computer taking several long seconds to reboot, despite having a multi-core, multi-gigahertz, hyper-threaded and pipelined CPU with multi-level cache and solid-state storage, is something that affects everyone, everywhere, every day, so it does in fact have quite a high impact.