ABSTRACT
HTA was influenced by a control theory model of human performance embodied in the idea of Test-Operate-Test-Exit or TOTE units (Miller et al. 1960). The essence of a TOTE unit is that it specifies a goal, represented by the set point of a control loop, and an action generation system controlled by feedback on the discrepancy between set point and current goal state. A nested hierachy control unit (‘operations’ in HTA terminology) is the essential feature of the analysis since goals can have many sub-goals and there is a parent-child relationship at each level in the hierarchy. The level of detail to which an analysis is taken is not fixed, as in both classical work study and recent HCI methods, but depends on whether or not the source of performance failure (or significant risk of failure) can be identified. HTA has been linked to many applications including personnel selection and manning, training, workplace layout and equipment design and this versatility is perhaps the main reason behind its success.
