Copyright 2003 by Dr. Gallimore, Wright State University Department of Biomedical, Industrial Engineering & Human Factors Engineering Task Analysis

Copyright 2003 by Dr. Gallimore, Wright State University

Department of Biomedical, Industrial Engineering & Human Factors Engineering

Task Analysis

Department of Biomedical, Human Factors, & Industrial Engineering


What is Task Analysis?

The study of what an operator (or team of operators) is required to do, in terms of actions and/or cognitive processes, to achieve a system goal. It provides the user with a “blueprint” of human involvement in a system.

Reference: Kirwan, B. and Ainsworth, L.K. (1992. A Guide to Task Analysis Bristol, PA: Taylor & Francis Inc.



Why Conduct Task Analyses?• Ensure system safety through hazard identification,

effective system design, human reliability assessment, and incident investigation

• Enhance productivity through determination of where to automate system processes, evaluation of staffing and training requirements, and identification of error potential

• Increase system availability by identification of maintenance demands, and requirements for maintenance support tools



When Is Task Analysis Done?

• In System DesignThroughout the life-cycle or the system: from initial

concept development, through design, to construction, commissioning, and operation (also in system decommissioning)

• In System EvaluationTo assess impact when system changes, or as part of

periodic reviews (audits or risk assessments)



Task Analysis Application Areas

• Allocation of functionAllocating functions between personnel and machines,

and defining extent of operator involvement in the control of the system

• Person specificationDefining characteristics and capability requirements of

personnel to enable to efficiently carry out the task



Task Analysis Application Areas cont.

• Staffing and job organizationDefining the number of staff required, the organization

of team members, communications requirements, and allocation of responsibility

• Task and interface designEnsuring adequate availability and design of information

displays, controls, and tools to enable the operator(s) to adequately carry out the task



Task Analysis Application Areas cont.

• Skills and knowledge acquisitionTraining and procedures design

• Performance assuranceAssessment of performance predicatively via human

reliability assessment, retrospectively via incident investigation or analysis, or concurrently via problem investigations



Task Analysis and System Life-Cycle

Human Factors Issue

Concept Spec.

System Def. Design Deploy Ops and Maint

Allocation of function

Best Poss Poss Check

Person specification

Review Check

Staffing Too soon Best Poss Check

Task and interface design

Too soon Best Best

Skills acquisition

Too soon Too soon Best Best Check

Performance assurance

Constantly

From Kirwan and Ainsworth, 1992



Task Analysis Techniques - Overview

Category Description

Task data collection techniques

Primarily used for collecting data on human- machine interactions, and which then feed into other techniques

Task description techniques

Structure collected information into systematic format. Formats may then serve either as reference material to enhance understanding of human –

machine involvement

Task simulation methods

Aim at compiling data on human involvement to create a dynamic model of task execution. Provides generic model of task performance (in time and

accuracy) based on individual task data

Task behavior assessment

methods

Identify what can go wrong that can lead to system failure, and often deal with hardware, software, and environmental events as well as human errors.

Derived from engineering risk assessment domains

Task requirement evaluation methods

Assess adequacy of facilities which operator(s) have available to support task execution, and directly assess the interface and facilitator designs (e.g.

training manuals)



Analysis Procedures

• Mission Analysis Function Determination

• Function Allocation

• Task Description / Identification

• Task Analysis



Mission Analysis (System Requirements Analysis)

• What is the system supposed to accomplish?• The analyst/designer needs to know -

– Specific Goals– Required Outputs– Required Inputs– System Capacities and Performance Requirements– Operating Environmental Factors– Constraints on System Operation



Mission Analysis Tools

• Mission Profile – Graphic Description (Example - Flight Profile)

• Mission Scenario– Verbal Description - Summarizes typical assumptions, environments, operations.

• Mission Segment– Time period of coherent activities with definite beginning and ending points.



Importance of Function & Task Analyses

Evaluate Human Factors Implications Design Requirements and ConstraintsWorkload Implications• Notes:1. Decompose to level where functions to be performed by system can be identified.2. Be careful that proposed design solution does not appear to be a function

description.



Determination of Functions•

Identify and Describe Functions - byDetermining Function Inputs and Outputs

Establishing Functional Performance Criteria

Preparing Functional Flow Diagrams

Function Examples:To Detect To RepairTo Analyze



Determination of Functions

Functions - Can beInstantaneous (Start Engine)Prolonged( Monitor Radar Screen)Complex (Analyze Equipment

Malfunction)



Function Performance Criteria

• Yardstick used to measure/predict whether or not the system/function meets the performance requirements.

• Criteria can range from gross to finely detailed.• Functional Performance Criteria must be stated in terms of those test results that must

be satisfied in order for the system/function to meet the performance requirements.• Provides the basis for preparing the Functional Flow Diagram.



Functional Flow Diagram

• Determine the functions that have already been allocated.• Describe the various different ways that each unallocated function might be

accomplished.• Establish the weighting criteria for comparing the alternatives.• Compare each of the alternative against one another.• Select the most cost-effective design.



Task Description / Identification

•

• Examine each selected design alternative.

• List in sequence all the actions that must be performed to accomplish the functional element.

• Categorize actions in terms of whether they areoperator or maintainer activities; and by thehardware/software subsystems to which they belong.

• Describe each action in terms of a behavioral verb (see next slide).

• Break tasks down into subordinate tasks by specifying inputs and outputsfor each task/subtask.



Behavioral Verbs

• ActionExample - to turn on, to monitor, to disassemble

• Equipment Acted UponExample - switch, motor, display

• Consequence of ActionExample - voltage display stabilized

• Stimulus that Initiates the ActionExample - pilot’s command



Behavioral Verbs (cont)

• Feedback Information Resulting form Task Performance

Example - aircraft heading 320 degrees

• Criterion of task accomplishmentExample - vehicle stopped/parked with 3 feet of

marker



Task Analysis

• Collect Information (See Table 1 Handouts)• Record Data (See Table 2, Figure 1 Handouts)• Analyze Data (See Table 3 Handouts)



Task Analysis Techniques

• Task Data Collection Methods– Activity sampling– Critical incident technique– Observational techniques– Questionnaires– Structured interviews– Verbal protocols



Task Analysis Techniques cont.

• Task description methods (charting and network)– Input-output diagrams– Process charts– Function flow diagrams– Information flow charts– Critical path analysis– Petri nets– Signal flow graphs




• Task requirements evaluation methods– Ergonomics checklists– Interface surveys




• Task description methods– Hierarchical task analysis– Link analysis– Operational sequence diagrams– Timeline analysis




• Task behavior assessment methods– Barrier and work safety analysis– Event trees– Failure modes and effects analysis– Fault trees– Hazard and operability analysis– Influence diagrams– Management oversight risk tree technique




• Task simulation methods– Computer modeling and simulation– Simulators and mock-ups– Table-top analysis– Walk-through and talk-through



HTA – A General-Purpose Task Analysis Technique

• Hierarchical Task Analysis (HTA)– Developed for use in training domain (Annett et al.,

1971)– Requires the analyst to establish conditions when

various subtasks should be carried out to meet a system’s goals

– Produces a hierarchy of operations and plans– Activities of human operator are linked directly to

system requirements



HTA Application

• For all stages of system life-cycle• Used to deal with:

– Interface design– Work organization– Facilitator design– Human error analysis



Basic Terms

• GoalsDesired states of systems under human control or supervision

• TasksMethods adopted to attain the goal, in any instance, which is

constrained by: availability and cost of materials; equipment and facilities demands; availability and cost of services; time constraints; legal obligations; and personnel preferences

• OperationsAny unit of behavior, no matter how long or short in duration, and no

matter how simple or complex in structure, which can be defined in terms of its objective



Basic Concepts

• Hierarchies of goals and sub-goalsGoals can be described at various levels of detail, thereby allowing

the nesting of goals (sub-goals)

• Plans and the organization of sub-goalsPlans specify condition when sub-goals should be carried out. Can

include sequences of actions or sets of actions conditional upon time or events

• Stopping rulesStop converting goals into plans and sub-operations when effort and

time is no longer justified. The rule may depend on the domain or particular task



Task AnalysisExample of Question Categories

• Design Questions• Manning Questions• Training Questions• Test and Evaluation Questions



Design Questions

• What tasks need to be performed?

• How critical is each task?

• In what sequence must the tasks be performed?

• What control activations are required?etc, etc, etc, etc



Manning Questions

• How many people are required to perform the task?

• What skill levels are required?



Training Questions

• On what behavioral dimensions are the tasks performed?

• How difficult or complex is each task?

• What information is required to perform the task?etc, etc, etc, etc



Test and Evaluation Questions

• What are the performance criteria for the task or job?

Documents

Copyright 2003 by Dr. Gallimore, Wright State University Department of Biomedical, Industrial Engineering & Human Factors Engineering Task Analysis