Definition
The FMEA score for how likely a given cause is to happen; it is scored against the cause, not against the failure mode and not against the effect.
In detail
Occurrence is scored cause by cause: a failure mode with three causes has three rows and three occurrence scores. It is the score most open to evidence — when process capability, defect records or downtime logs exist, do not rate it from memory. Lowering occurrence means changing the process or the design, which is more fundamental and more expensive than adding an inspection (that lowers detection). The courseware warns that a standing team carries the rating basis of its last project into the next one, so the same people on a new project must align the scale first.
Example in practice
The team lists three causes for insufficient press-fit force. Looking up the table from six months of logs, fixture wear shows up in about 20 units out of roughly 1,600 produced per month (about 1/80, or 12,500 PPM), which rates occurrence 6; after a fixture with a wear alarm is installed it is re-rated 2, while severity on the same row stays unchanged.