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Function Allocation

Function allocation (also known as task allocation) is a classic human factors method for deciding whether a particular function will be accomplished by a person, technology (hardware or software) or some mix of person and technology. To do this, the investigator considers error rates, fatigue, costs, hazards, technological feasibility, human values, ethical issues, and the desire of people to perform the function.


Related Links

Jordan, N. (1963). Allocation of functions between man and machines in automated systems. Journal of Applied Psychology, 47, 161-165.

Kantowitz, B.H., & Sorkin, R.D. (1987). Allocation of functions. In: G. Salvendy (Ed.). Handbook of human factors. New York: Wiley.

Sharit, J. (1997). Allocation of functions. In G. Salvendy, (Ed.), Handbook of Human Factors and Ergonomics (2nd ed.). New York: John Wiley.

Sujan, MA. and Pasquini, A. (1998) Allocating Tasks between Humans and Machines in Complex Systems. 4th International Conference on Achieving Quality in Software, Venezia, 1998


Fitts, P. (1951). Human engineering for an effective air-navigation and traffic-control systems. Columbus, OH: Ohio State University Foundation.

Authoritative References

Bekey, G.A. (1970). The human operator in control systems. In: K.B. DeGreene (Ed.). Systems psychology. New York: McGraw-Hill.

Chapanis, A. (1970). Human factors in systems engineering. In: K.B. DeGreene (Ed.). Systems psychology. New York: McGraw-Hill.

Ip, W.K., Damodaran, L., Olphert, C.W. & Maguire, M.C. (1990). The use of task allocation charts in system design - a critical appraisal. In D. Diaper, G. Cockton, D. Gilmore & B. Shackel, Eds. Human-Computer Interaction INTERACT'90, pp. 289-294. Amsterdam: North-Holland.

Older, M.T., Waterson, P.E. and Clegg C.,W. (1997) A critical assessment of task allocation methods and their applicability. Ergonomics, 40(2): 151-171.

Detailed description

Benefits, Advantages and Disadvantages


  • Function allocation is useful for determining the degree of automation that is optimal for a system.


  • Function allocation guidelines are often simplistic and provide only limited heuristics for allocating functions among people, hardware, and software.
  • Function allocation can affect important human values. For example, automated systems that do not allow much human intervention can lower user satisfaction.

Appropriate Uses

Tasks should be allocated to humans and machines in a way that best combines human skills with automation to achieve task goals, while supporting human needs.

How To


Prior information

Context of use analysis and task analysis should be used to identify the task structure and demands, the knowledge needed to perform the tasks, environmental constraints, functional and safety requirements, and any other relevant issues.

Mandatory allocation

Mandatory allocation can be identified from the task model, e.g.

  • Allocate functions to humans when there are technical limitations, ethical constraints, or safety considerations.
  • Allocate functions to machines when task demands exceed human capabilities or when the system must be operated in a hostile environment

Provisional allocation

Permanently allocate tasks based on factors such as task criticality, cost, training or knowledge requirements, or task unpredictability.

Dynamically allocate tasks based on factors such as human workload, the need for cognitive support, individual differences in users, changing capacity of the user, or organisational learning.

Jobs must be designed from the tasks based on factors such as responsibility, task variety, interference between and within tasks, communication between users, and individual capability.


The provisional allocations and jobs should be evaluated based on factors such as: safety, system performance, usability, cost, job satisfaction and human well-being, acceptance by users, management and society and social impact. The evaluation findings should be used to review and revise the provisional allocations which should then be re-evaluated.

(This procedure is based on Sujan & Pasquini, 1998.)

Materials Needed

Paul Fitts (1951) published an early list of functions (the Fitts' list) that were performed better by humans and functions that were performed better by machines. As technoogy has improved, the function allocation lists have been upgraded to take advantage of new machine capabilities like new sensors, advanced software, and better intelligence.

Common Problems

  • Users of an automated system may rely too heavily on automation and fail to monitor the system adequately.
  • Where there is dynamic allocation of functions between software and people (autopilots or crash avoidance systems in cars) when does the software allow the person to override the automation? Does the system know when someone is fatigued or when the driver is an expert?

Next Steps

The prototypes produced for evaluation of task allocation can be included as part of the iterative design process. This is followed by implementation.



Lifecycle: Requirements
Sources and contributors: 
Chauncey Wilson and Nigel Bevan (from UsabilityNet).
Released: 2009-06
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