Hierarchical task analysis (HTA) is a widely used type of Task analysis where a high-level task is decomposed into a hierarchy of subtasks. An HTA is sometimes referred to as a hierarchical decomposition.
Benefits, Advantages and Disadvantages
Although HTA has been used for over 40 years, it is still widely used in industry because it is simple and straightforward. The results of an HTA is a starting point for more detailed modeling methods, like GOMS.
When used in large project, HTA requires a lot of overhead work to revise / maintain task numbers and plans as tasks are edited and moved within the hierarchy. Also, it is difficult to synchronize the graphical and textual representations.
HTA representation consists of a hierarchy of tasks, sub-tasks and actions together with plans that describe the ordering and conditions of task performance. The plan is enabling the analyst to describe sequential, conditional and iterative tasks.
The decomposition in detail is done according to the P x C rule that estimates the efficiency of going on with the analysis based on the probability of inadequate performance and the cost of the inadequate performance. Therefore, further decomposition of tasks which requires extra effort of analysis is done only when there are reasons to estimate that current performance is not acceptable.
Typical reasons are error prone situation that could lead to serious consequences such as: inconsistent interaction methods, problems with learning the task delegation or execution time constraints. In all cases cost-benefit estimation is useful in order to avoid waste of time.
The method provides with both graphical and tabular representations.
Data Analysis and Reporting
Several tools have been developed to support HTA. See, for example TaskArchitect.