The likelihood or probability for a risk event must always be between zero and one. Qualitative risk assessment depends on defined probability ranges between these limits, using defined percentages.
Projects may use two, three, or more ranges for assessment, trading off between fewer (to simplify the process) or more (to improve precision). Three ranges offer a reasonable balance between obtaining team agreement and ability to sort potential risks by severity. Risk assessment using this method uses ranges of high, moderate, and low, often defined as:
High: 50 percent or higher probability
Moderate: Between 10 and 50 percent probability
Low: Less than 10 percent probability
Additional probability ranges may be defined, with associated ...