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 training Display area Control knobs/switches

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: 5 th percentile female to 95 th 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 log 2 (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