Performance-Based

With performance-based measures, a portion or all of a user's task is selected for objective and quantitative measurement. Traditionally, performance-based measurements have included speed and accuracy data. Speed can be reaction time either to perceive an event or to initiate a response. Accuracy can be whether or not a signal is perceived and if an appropriate response is made. Sometimes a secondary task measure is introduced in order to determine if spare performance capacity exists.

• Primary Task Measure - This is usually the most important component of a particular job or a job component that is suspected of unduly increasing workload. Primary task measures are used to discriminate cognitive overload from non-overload conditions. These measures are particularly useful in assessing design options to determine if user performance is acceptable.
• Secondary Task Measure - Secondary tasks are measured to determine if reserve cognitive and performance capacity is available in addition to primary task performance. These measures are used to evaluate the potential for overload conditions among design options.

Secondary Tasks Determine Reserve Capacity

Performance-based measures can be selected and instrumented so as to be non-intrusive to the user. However, it is difficult to take such measures in some environments such as in the cockpit or in air traffic control operations. Therefore, such measures tend to be used with prototypes or simulators. For this reason, it may be difficult to use performance measures in early design phases.