Glossary · 3 · Tasks and minimalism
Hierarchical task analysis (HTA)
Also known as: HTA, Technical task analysis
German: hierarchische Aufgabenanalyse
In human factors, hierarchical task analysis (HTA) describes a task as a hierarchy of goals, subgoals and operations, linked by plans that state when and in which order the subordinate operations are carried out; it was developed by John Annett and Keith Duncan in the late 1960s.
- Technical documentation
- Task analysis
- Human factors
In one sentence
Hierarchical task analysis (HTA) breaks a task into goals, subgoals and operations, linked by plans that state order and conditions.
Example
Goal 0 'Change the format of the labeler' breaks down into 1 stop and secure, 2 change the reel, 3 adjust the guides, 4 test run; plan 0: do 1–4 in order, repeat 3–4 until the test label is within tolerance.
The informal label "technical task analysis" is sometimes used for this lens in documentation practice; it is not a separate method.
How it applies
- Plans become procedures: Each plan states the order and conditions of operations — procedural (do 1 then 2), conditional (if the alarm is on, do 3), iterative (repeat until within tolerance). In instructions they become the step sequence, the preconditions and the expected results of a procedure, for example in a DITA task.
- Stopping rule: Annett and Duncan proposed stopping the decomposition where the probability of inadequate performance multiplied by its cost (P × C) is acceptable. For documentation this marks where a step needs no further detail and where it needs a warning or a check.
- Training and error analysis: HTA is a common basis for a training needs analysis and for analyzing human error step by step.
- Limits: HTA shows steps and plans, not the knowledge and judgment behind them, nor the handovers between people. Task analysis results never prove that a product or a document is safe or compliant.
HTA vs. cognitive and team task analysis
HTA asks what is done in which order. Cognitive task analysis asks what a person has to know, notice and decide to do it; team task analysis asks which parts depend on several people and how they hand over. The three are lenses on the same task, not competing methods; see the context card Task analysis lenses.