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Human factors in the system life cycle. The human factors engineering process Research Model Define requirements Design Evaluation This is an iterative process. The system design life cycle front-end analysis conceptual design iterative design and testing design of support materials

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human factors in the system life cycle
Human factors in the system life cycle
  • The human factors engineering process
    • Research
    • Model
    • Define requirements
    • Design
    • Evaluation
  • This is an iterative process
  • The system design life cycle
    • front-end analysis
    • conceptual design
    • iterative design and testing
    • design of support materials
    • system production
    • implementation & evaluation
    • operation & maintenance
    • system disposal
  • This is an iterative process
tools of hf design
Tools of HF design
  • Design data:
    • anthropometric data, design data compendiums, standards, principles & guidelines, etc.
    • e.g., Human Engineering Design Data Digest, Department of Defense Human Factors Engineering Technical Advisory Group (April 2000).
  • Research methods
  • Modeling
  • Engineering analysis methods
    • Workload, safety, simulation, etc.
    • Use to derive system requirements
building models
Building models
  • Part 1: Models good for defining system and user requirements
    • Affinity diagrams
    • Flow model
    • Cultural model
    • Sequence model
    • Physical model
    • Artifact model
    • Source:

H. Beyer and K. Holtzblatt (1999), Contextual Design : A Customer-Centered Approach to Systems Designs. San Francisco, CA: Morgan Kaufmann.

Note: for more details on the following example, you should visit the InContext website at and choose the “Design Resources” link at the top, then to “CDTools™,” then “CDTools™ Resources,” and finally “Shopping Data Browser” on the left.

affinity diagram a good starting point
Affinity Diagram – a good starting point
  • Use the Post-It notes to record insights and quotes from your research and observations.
    • One phrase or quote per note.
    • Write big enough for all to see.
  • Post the notes on the wall.
  • “Walk the wall” and rearrange the notes into like categories.
  • When everyone is agreed on the categories, give each category a meaningful name and summarize the findings.
  • Use the affinity diagram to generate design ideas, identify requirements, and inform other models.
flow model
Flow model
  • Draw the primary user of the system in the center of the page.
  • Use Post-It notes to add other users, people, “roles,” and physical objects as needed to define flows of work and information.
  • Use annotated lines and arrows to indicate flows of information or work.
  • Indicate opportunities for “breakdowns” in communications or work flow.
  • Use the model to add to or refine requirements, define key interactions, and identify communication modes and methods.
cultural model
Cultural model
  • Draw a circle representing the primary user in center.
  • Draw overlapping and concentric circles representing other entities that affect the primary user.
  • Draw arrows indicating influences, constraints, and expectations.
  • Identify individual and pervasive values that affect how the user will approach the task.
  • Use the model to define subtleties that should affect system design.
sequence model
Sequence model
  • Define specific steps the user goes through to accomplish the task.
  • Identify strategies and decision points.
  • Identify breakdowns that make the task difficult to complete.
  • Where appropriate, identify options and alternative strategies.
  • Use the model to further define requirements, identify design opportunities, and begin to define potential interaction methods.
  • (We’ll come back to this later …)
physical model
Physical model
  • Diagram in detail the physical space in which the task is performed.
  • Identify both “official” and “unofficial” designation of locations.
  • Identify paths taken through the space during task performance.
  • Define how users use the space to accomplish the task.
  • Identify breakdowns where the physical space inhibits task performance.
  • Use the model to develop system design requirements and opportunities.
artifact model
Artifact model
  • Draw or diagram the artifacts used to accomplish the task.
  • Specify the user’s intent in using the artifact.
  • If necessary, identify variants of the artifacts.
  • Identify potential breakdowns where the artifact inhibits task performance.
  • Use the model to define user requirements and identify potential design directions.
building models1
Building models
  • Part 2: Models good for defining interaction
    • HTA
    • GOMS
    • OFM
  • Process
    • Step 1: develop an understanding of the user and task(interviews, questionnaires, observation, etc.)
    • Step 2: decide on a modeling framework
    • Step 3: build the model
    • Step 4: test/refine/modify
    • (Step 5: Use the model to drive design, testing, etc.)
making a pbj sandwich hierarchical task analysis hta
Making a PBJ sandwich: Hierarchical Task Analysis (HTA)

1. Describe top-level goal:

  • “0. Make a peanut butter and jelly sandwich.”

2. Develop a plan for achieving that goal (including “error handling”):

  • Plan 0: Do 1-5, in order. If some ingredient is missing, do 5.
    • “1. Get plate and knife.
    • 2. Collect ingredients.
    • 3. Assemble sandwich.
    • 4. Eat and enjoy.
    • 5. Put ingredients away.”
making a pbj sandwich hta
Making a PBJ sandwich: HTA

3. For each step in the plan, decide if more detail is required. Continue until sufficient detail is defined.

e.g., for step 1 …

  • Plan 1: Do 1-3; if no clean implements, do 4.
    • 1.1 Go to cabinet and retrieve 1 plate.
    • 1.2 Go to drawer and retrieve 1 knife.
    • 1.3 Take knife and plate to table.
    • 1.4 Wash knife/plate as necessary.
your turn
Your turn …
  • Continue the HTA for:
    • Plan 2
    • Plan 3
    • Plan 5
  • Discuss – which parts of your plan need more specification?
making a pbj sandwich goms goals operators methods selection rules
Making a PBJ sandwich: GOMS (Goals, Operators, Methods, & Selection rules)

1. Describe top-level goal:

  • “GOAL: Make a peanut butter and jelly sandwich.”

2. Describe a methods for achieving that goal (including selection rules and alternatives):

    • GOAL: Get plate and knife.
    • GOAL: Collect ingredients.
    • GOAL: Assemble sandwich.
    • Eat and enjoy.
    • GOAL: Put ingredients away.
making a pbj sandwich goms
Making a PBJ sandwich: GOMS

3. For each “GOAL” in the method, describe a more detailed method.

e.g., •GOAL: Collect ingredients.

• • GOAL: Get bread.

• • GOAL: Get peanut butter.

• • GOAL: Get jelly.

• • • [Selection Rule:

Goto refrigerator

Goto pantry ]

making a pbj sandwich goms1
Making a PBJ sandwich: GOMS

4. Continue until desired/necessary level of detail.

5. Use the (HTA or GOMS) model to:

  • Design documentation.
  • Predict performance.
  • Evaluate device/task designs.
  • Design.
modeling more complex tasks the operator function model ofm
Modeling more complex tasks: the Operator Function Model (OFM)
  • Hierarchical/Heterarchical task decomposition
    • Activities are decomposed hierarchically (as in HTA and GOMS)
      • Functions - highest-level activities (e.g., navigate, communicate, and aviate are pilot functions)
      • Subfunctions - activities required to accomplish functions
      • Task - lower level (more specific) activities to accomplish functions or subfunctions
      • Actions - manual, cognitive, or perceptual
    • Heterarchical structure accounts for concurrent activities, usually defined at the same level.
      • Operators may choose from among these activities or the activities may result from system state(s).
ofm example chinese dinner party
OFM example: Chinese dinner party

Steps (from Mitchell, 1998):

1. “Prepare a high-level written description of the system of interest …”

ofm example chinese dinner party1
OFM example: Chinese dinner party

Steps (from Mitchell, 1998):

2. Identify the high-level activities the operator performs.

3. Define the heterarchy, specifying conditions for transitioning, initiating, or terminating activities.

ofm example chinese dinner party2
OFM example: Chinese dinner party

4. Define the hierarchy, including conditions that start or end activities.

5. Validate the model. (Emphasis on direct observation, mapping actions into the model, resolving discrepancies.)

6. Refine the model as the system evolves.

summary user task modeling
Summary: User/Task Modeling
  • What is a user/task model?
    • Model - “a mathematical/physical system, obeying specific rules and conditions, whose behavior is used to understand a real (physical, biological, human-technical, etc.) system to which it is analogous in certain respects.”(Bailey, 1989)
    • A “good model” is one that adequately represents and can be used to generate testable hypotheses about the underlying system.
    • User/task models - specifically focus on modeling the user’s goals and objectives, as well as his/her understanding of the task.
summary user task modeling1
Summary: User/Task Modeling
  • Dimensions of models …
    • Conceptual ………………. Computational
    • Descriptive ………………..Normative
    • Levels of specificity
      • Device …..….. task ……... meta-cognitive
using models in system design
Using models in system design

Define Req’ts.

  • A basis for defining requirements
    • Identify information and action requirements, as well as potential sources of difficulty for the operator/user (high workload, ambiguities, etc.), task importance, who else is involved, etc.
    • The more detailed the model, the more useful for design
    • Design decisions may be used to refine or modify the model
  • A basis for test & evaluation
    • Heuristic evaluation – does the system as designed support the activity you modeled?
    • Defining testing procedures, metrics, etc.