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Usability  > User-Centered Design Steps > Step 5 - 5 of 6
 
 


Step 5 - Analyze and Design Tasks

In this step, the human functions allocated in STEP 4 are aggregated into jobs by  assignment to operators, maintainers, supervisors, or other users.  Within each "job," functions are decomposed into tasks.  Human-centered design uses a decision analysis approach for task design that identifies for each task:  the cues that alert the user that a decision or action is needed, the specific decision or action required, information to support the decision or action, the means of decision or action implementation, and the criteria for determining task completeness and performance accuracy.  The sub-steps for task design and development are as follows:

 

  • Aggregate functions into jobs.  Analyze human functions and assign to appropriate human performer:  operator, maintainer, supervisor, operational manager, remote monitor, or other job position.

  • Break down functions into tasks and sub-tasks.  Within each job position, decompose each function into tasks and into sub-tasks, if necessary.  For each, derive estimates of duration, frequency, and priority.

  • Define task sequence.  Identify the sequence of task/subtask performance.  Then, associate human task and equipment task sequences and define the interrelationships between them, including timing and results.  Operational Sequence Diagrams (OSDs) are often used for this purpose.

  • Define task initiation and completion criteria.  Define, for each human task and subtask, the events (internal or external), actions, or information provision required for task initiation, continuance, or termination.  Add this data to the OSDs or other documentation methodology used to define task sequence.

  • Estimate accuracy and success probability.  For each human task and subtask, estimate performance accuracy and success probability.

  • Estimate error and failure results.  Identify the types of errors, possible for the human to commit for each task and subtask, and the likely outcome of these errors.  Include effects on the system or its components and on other functions and tasks.  Perform the same for failure to perform or complete a task or subtask.

  • Identify critical tasks.  Identify and rigorously analyze tasks considered "critical" to protecting personnel and system safety.  Assess for error and failure results and tag for fault tolerant or fault resistant interface design.

This step in Human-Centered design requires heavy involvement of Human Factors specialists leading and facilitating user groups.  Task design and analysis is the foundation for human-to-system interface and workstation design--Step 6.

  
 

 
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