Human Factors Issues

Chapter 9

Human Factors

= ergonomics WWII based – military

significance… … a necessary part of medical

device design…

What is Human Factors?

Application of the scientific knowledge of human capabilities and limitations to the design of systems and equipment to produce products with the most efficient, safe, effective, and reliable operation

Human Factors

Interface points Environment Skill level of user Interaction between:

Human element Hardware element Software element

Refrigerator Example

Human Element Memory

Long term Short term

Thinking and reasoning Visual perception Dialogue construction Individual skill level Individual sophistication

Hardware Element

Size limitations Location of

controls

Compatibility with other equipment

Potential need for

portability

Possible user trainin

g

Display area

Control knobs/switche

s

Example

Using 5% female to 95% male reach data, design an anesthesia machine layout….

What constraints does this put on the design?

What % overall of the population would be served?

Software Element

Simple, reliable data

entry

Menu driven

Displays must not be overcrowded

Dialogue must be

jargon-free

Feedback to users

Human Factors Process Analytic process that focuses on

device objectives Design and development process

that converts results of analyses into detailed equipment features

Test and evaluation process which verifies that development process satisfies constraints

Steps in Human Factors Process

Planning Analysis Conduct user studies

Observations Interviews Focus groups Task analysis Benchmark usability

tests User profile Setup advisory panel

Crucial Pieces of Human Factors Process

Safety

Should reflect system and personnel safety factors

Failures Fail safe Failure indications

Standards- ANSI, AAMI, ISO

Documentation Written to meet needs of various

target populations Study capability and information

needs of documentation users Mental abilities Physical abilities Previous experience Understanding of general operation Special needs of environment

Attempt to avoid

this!

Anthropometry

Science of measuring human body and its parts and functional capacities

Range of values: 5th percentile female to 95th percentile male

Functional dimensions Psychological elements Workstation design considerations

Labeling

Labels should be clear and direct Controls, displays, and other

equipment that must be located should be clearly marked

Receptacles and connectors should be marked with intended function or connection

Hazard warnings should be prominent

Labeling?

Software

Every user input should consistently produce some perceptible response from the computer

Log-on should be automatically completed before any operation

Allow for orderly shutdown in case of failure

Data Entry Consistent data entry

transactions Minimize user input

actions Feedback to user about

acceptance or rejection of an entry

Ability to change entry after it has been added

Feedback

Present status, information, confirmation, and verification throughout the interaction

Standby should be accompanied by ‘WAIT’ message

Feedback should be self-explanatory

Prompts

Commands, error messages, system capabilities, and procedures should be explained with prompts or help instructions

Missing data/aborting changes should be prompted

Factual and informative dialogue Displayed in standardized area

Defaults

Currently defined default values should be provides and automatically displayed

User should be prompted for acceptance of defaults

Users should be able to set their own default

Fitt’s Law

T = a + b log2 (D/W + 1) where T = the average time taken to complete the

movement A = the start/stop time of the device B = the inherent speed of the device D = the distance from the starting point to the center

of the target W = the width of the target measured along the axis

of motion.

Outcome of Fitts’ Law:

Bigger buttons are better Edges/corners are easiest Pop-up menus are easier than pull-

down Pies are better than boxes