“Used to estimate the likelihood of each undesired event identified at the hazard identification stage. The purpose of frequency analysis is to determine the frequency of each of the undesired events or accident scenarios identified at the hazard identification stage. Three basic approaches are commonly taken: a) Use relevant historical data to determine the frequency; b) Predict event frequencies using techniques; c) Use expert judgment.”
Reference: IEC60300‐3‐9 (1995), Dependability Management’‐’Part 3: Application Guide – Section 9: Risk Analysis of Technological Systems, CEI/IEC 60300‐3‐9:1995, International Electrotechnical Commission, Geneva.
Note: Frequency is used here as probability of occurrence of an event over a certain time period, usually a year.