Technique for Human Error Rate Prediction THERP

Technique for Human Error Rate Prediction (THERP) 

Swain and Rook developed Technique for Human Error Rate Prediction (THERP) in 1961 to quantify human error rates due to problems of equipment unreliability, operational procedures, and any other system characteristic that could influence human behavior 

THERP is usually modeled using a probability tree. Each branch represents a task analysis showing the flow of task behaviors and other associations. A probability is assigned based on the event s occurrence or nonoccurrence. 

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S.2.9 Technique for Human Error Rate Prediction (THERP)... 

Technique for human error-rate prediction (THERP) Structure methodology for modeling human error and task completion in terms of probabilities Predicts human error and task completion probabiUties using a human performance database and expert judgments... 

The technique for human error-rate prediction (THERP) [ Swain and Guttmann, 1980] is a widely applied human reliability method (Meister, 1984] used to predict human error rates (i.e., probabilities) and the consequences of human errors. The method relies on conducting a task analysis. Estimates of the likelihood of human errors and the likelihood that errors will be undetected are assigned to tasks from available human performance databases and expert judgments. The consequences of uncorrected errors are estimated from models of the system. An event tree is used to track and assign conditional probabilities of error throughout a sequence of activities. 

For analyzing and quantifying human error nowadays mostly the Technique for Human Error Rate Prediction (THERP) procedure is applied. The method is documented in [52] along with a comprehensive data collection. Despite numerous further developments in the field it remains the procedure most suitable for practical applications. 

In current HRA practice, the most widely used dependence assessment method is the dependence model and method included in the Technique for Human Error Rate Prediction (THERP) HRA method (Swain Guttman 1983). The current practice has however a number of weaknesses. Often, the assessment is performed based on direct expert judgment so that the results lack traceability and repeatabftity. In some cases, simphfied expert elicitation approaches, hke decision trees (Gertman et al. 2004, Juluis et al. 2005) are used, which however are not based on a transparent expert ehcitation process (Podofillini et al., in prep.). 

There are a number of methods for evaluating the probability of human error. Two of the better-known methods are the Technique for Human Error Rate Prediction (THERP) (Reference NUREG/CR-1278) and the Accident Sequence Evaluation Program Human Reliability Analysis Procedure (Reference NUREG/CR-4772). Error rates are usually established on a per-demand basis. 

The Technique for Human Error Rate Prediction (THERP) was developed by Swain and Guttman (1983) to evaluate the probability of human error within specific tasks. THERP uses a fault tree approach to model Human Error Probabilities (HEP), but also attempts to account for other factors in the environment that may influence these probabilities. These factors are referred to as Performance Shaping Eactors (PSE). The probabilities used in THERP can either be generated by the analyst, usually from simulator data, or can be taken from tables generated by Swain and Guttman from available data and expert judgement. 

Technique for Human Error Rate Prediction, (THERP), for the response phase. The aim of this methodology is to calculate the probability of the successful performance of the necessary activities for the completion of a task. 

In the process of risk and human reliability assessment, there are various methods to be used, such as Cognitive Reliability and Error Analysis Model (CREAM), A Technique for Human Error Analysis (ATHENA), and Technique for Human Error Rate Prediction (THERP). 

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