Task analysis
Task analysis is the analysis of  how a task is accomplished,  including a detailed description of both manual and mental activities, task and element durations, task frequency, task allocation, task complexity, environmental conditions, necessary clothing and equipment, and any other unique factors involved in or required for one or more people to perform a given task. Task analysis emerged from research in applied behavior analysis and still has considerable research in that area.
Information from a task analysis can then be used for many purposes, such as personnel selection and training, tool or equipment design, procedure design (e.g., design of checklists or decision support systems) and automation.
The term "task" is often used interchangeably with activity or process.  Task analysis often results in a hierarchical representation of what steps it takes to perform a task for which there is a goal and for which there is some lowest-level "action" that is performed.  Task analysis is often performed by human factors professionals.
Task analysis may be of manual tasks, such as bricklaying, and be analyzed as time and motion studies using concepts from industrial engineering.  Cognitive task analysis is applied to modern work environments such as supervisory control where little physical works occurs, but the tasks are more related to  situation assessment, decision making, and response planning and execution.
Task analysis is also used in education. It is a model that is applied to classroom tasks to discover which curriculum components are well matched to the capabilities of students with learning disabilities and which task modification might be necessary. It discovers which tasks a person hasn't mastered, and the information processing demands of tasks that are easy or problematic.  In behavior modification, it is a breakdown of a complex behavioral sequence into steps.  This often serves as the basis for Chaining.

# Task analysis: data collection
The analyst will often directly observe tasks performed by practitioners (as in  ethnographic studies) and may audio-tape and videotape actual task performance.  A more controlled study may be done in a laboratory, as in experimental psychology, where the practitioner may work with a simulation of the real task environment.  An analysis of actual work procedures, manuals, etc. is also valuable.

# Computational models of cognitive task performance

# Task analysis versus Work Domain Analysis
If task analysis is likened to a set of instructions on how to navigate from point A to point B, then work domain analysis (WDA) is like having a map of the terrain that includes Point A and Point B (see Lintern, 2005).   WDA is broader and focuses on the environmental constraints and opportunities for behavior, as in Gibsonian ecological psychology and ecological interface design.

# Task analysis and documentation
Since the 1980s, a major change in technical documentation has been to emphasize the tasks performed with a system rather than documenting the system itself. (Hackos and Redish, 1998) In software documentation particularly, long printed technical manuals that exhaustively describe every function of the software are being replaced by online help organized into tasks. This is part of the new emphasis on usability and user-centered design rather than system/software/product design.
According to the historian of technical communication, R. John Brockmann, this task orientation in technical documentation began with publishing guidelines issued by IBM in the late 1980s. Later IBM studies led to John Carroll's theory of minimalism in the 1990s.
With the development of XML as a markup language suitable for both print and online documentation (replacing SGML with its focus on print), IBM developed the Darwin Information Typing Architecture XML standard in 2000. Now an OASIS standard, DITA has a strong emphasis on task analysis. Its three basic information types are Task, Concept, and Reference. Tasks are analyzed into steps, with a main goal of identifying steps that are reusable in multiple tasks.