Technique For Human Error Rate Prediction - Disadvantages of THERP

Disadvantages of THERP

• THERP analysis is very resource intensive, and may require a large amount of effort to produce reliable HEP values. This can be controlled by ensuring an accurate assessment of the level of work required in the analysis of each stage.
• The technique does not lend itself to system improvement. Compared to some other Human Reliability Assessment tools such as HEART, THERP is a relatively unsophisticated tool as the range of PSFs considered is generally low and the underlying psychological causes of errors are not identified.
• With regards to the consistency of the technique, large discrepancies have been found in practice with regards to different analysts assessment of the risk associated with the same tasks. Such discrepancies may have arisen from either the process mapping of the tasks in question or in the estimation of the HEPs associated with each of the tasks through the use of THERP tables compared to, for example, expert judgement or the application of PSFs. .Missing reference 6
• The methodology fails to provide guidance to the assessor in how to model the impact of PSFs and the influence of the situation on the errors being assessed.
• The THERP HRAETs implicitly assume that each sub-task’s HEP is independent from all others i.e. the HRAET does not update itself in the event that an operator takes a sub-optimal route through the task path. This is reinforced by the HEP being merely reduced by the chance of recovery from a mistake, rather than by introducing alternative (i.e. sub-optimal) “success” routes into the event-tree, which could allow for Bayesian updating of subsequent HEPs.
• THERP is a “first generation” HRA tool, and in common with other such tools has been criticised for not taking adequate account of context Missing reference