Table 1.

Probability of an Occurrence

Score	Probability	Description
5	Most Certain	Events are expected to occur or will occur periodically with high probability. More than once in a year
4	Likely	Events have a probability of happening. Once in 1–3 years
3	Possible	Events are likely to occur. Once in 3–5 years
2	Unlikely	Events can happen. Once in 5–10 years
1	Rare	Events are not likely to occur or will only occur in exceptional circumstances. Once in 10 or more years