From such analyses measures can then be taken to reduce the likelihood of errors occurring within a system and therefore lead to an improvement in the overall levels of safety.
It is grounded on the premise that people cannot recall or are unable to estimate with certainty, the probability of a given event occurring.
Moreover, within the context of use, it is unusual for a single individual to possess all the required information and expertise to be able to solely estimate, in an accurate manner, the human reliability in question.
This allows for some information sharing, whilst avoiding most group-led biases; however there still remains the problem of a lack of discussion.
By this means, information-sharing is superior, and group domination is mitigated by having the experts separately come to their own conclusion before aggregating the HEP scores.
This is the most group-centred approach and requires that the group must come to a consensus on the HEP estimates through discussion and mutual agreement.
This method maximises knowledge sharing and the exchange of ideas and also promotes equal opportunity to participate in discussion.
However, it can also prove to be logistically awkward to co-ordinate as it requires that all experts be together in the same location in order for the discussion to take place.
Due to this technicality, personalities and other biasing mechanisms such as overconfidence, recent availability and anchoring may become a factor, thus increasing the potential for the results to be skewed.
The correct number of experts is dependent upon what seems most practicable, while considering any constraints such as spatial and financial availability.
The optimal level of detail will be governed by the nature of the task under consideration and the required use of the final HEP estimation.
Calculate inter-judge consistency This is a method by which the differences in the HEP estimates of individual experts can be compared; a statistical formulation is used for such purposes.
In this example, absolute probability judgement was utilised by Eurocontrol, at the experimental centre in Brétigny-sur-Orge Paris, using a group consensus methodology.
During the duration of the session it was revealed that the ease with which the experts were able to arrive at a consensus was low with regards to the differing estimates of the various HEP values.