Task Analysis: Understanding How People Think and Behave

An MD&DI January 1997 Feature Article

DESIGNER'S TOOLBOX

Task analysis is a highly effective tool for studying the way peoplethink about and use a product. This tool has its roots in the early time-motionstudies of Gilbreth and Taylor. F. B. Gilbreth, a contractor, observed that notwo bricklayers used the same technique to lay a brick. Using a time-motionanalysis technique, he was able to identify inefficiencies and therefore reducethe number of discrete motions used to lay a brick--on average from 18 to 4.25.Today the technique remains the same, although the tools are more sophisticated.

Task analysis can be used to help redesign medical devices such as aventilator system for a neonatal intensive-care unit (see figure below). Thissystem consists of a ventilator, humidifier, oxygen analyzer, alarm unit, andpatient interface device. An optimal design enables a user to operate thesecomponents with the fewest movements.

Figure 1. Depictions of the primary system functions of a ventilator and a map of the device's 24 links.

LEVELS OF ANALYSIS

The task analysis tool has three levels: general task analysis, motionanalysis, and link analysis. Each successive level builds on the informationgenerated in the previous one.

General Task Analysis. General task analysis is a macrolevelinventory of the performed tasks. At this level, the designer defines all tasksand maps their sequence and interactions. On a spreadsheet, the behaviors,responses, and observations can be scored based on their frequency. This stepcan help researchers identify inefficiencies and problems, such as twosuccessive tasks being too far apart.

Motion Analysis. The second level evaluates the user's body postureand motion paths. The figure below depicts a map of the physical paths of auser's hands to illustrate the movement and frequency of each task and itsinterdependence with the others. The six-pointed bold-line overlay on the leftindicates six subtasks that compose a primary task. Because all users do notmove in the same way, it is best to test different users to identify variations.Researchers typically begin with about 25 subjects and add more as needed.

Link Analysis. Link analysis graphically depicts relationshipsbetween tasks. It identifies inefficient sequences and repetitive motions. Thisanalysis links tasks together in order of importance based on their duration,frequency, and sequence. Use of this analysis on the tasks in the figureidentifies 24 links and illustrates inefficient placement of controls. Forexample, nodes 6, 7, 12, 11, 5, 8, 9, 22, 21, and 16 are clustered, indicatingthat a redesigned system should organize and consolidate these controls into asingle functional ar- ray. Link analysis can also be conducted on specificsubtasks. For example, the ventilator has two modes of operation. Plots of eachmode could illustrate a logical left-to-right and top-to-bottom layout ofcontrols based on their impor- tance and frequency.

IMPROVING DESIGN

The task analysis technique is a powerful tool that can be used tointegrate into the design process how people use a product. This techniqueprovides the following information about the product studied:

Through use of these results in the design process, a product can bedeveloped that incorporates the most efficient path for users. The resultingredesigned device should be easier to use and better organized than theoriginal.

Bryce Rutter is principal of the Metaphase Design Group.

Copyright © 1997 Medical Device & Diagnostic Industry