Human factors engineering is based upon meaningful measurement of behavioral data. To arrive at useful conclusions about users' behavior, we must decide which data are relevant to our questions and how to measure them.
According to The American Heritage Dictionary, the primary meaning of data is "Information, especially information organized for analysis or used as the basis for a decision." This is the meaning we refer to when we use the term data. Some of the data we collect are quantifiable and can be measured numerically. A good example would be the number of times a participant used the Back button on his or her Web browser during a task. However, some of the behavioral observations we make are qualitative in nature and cannot be best expressed in numbers. These observations are valuable data as well.
Measurement is a process of quantifying objects or events by assigning numbers to them in a consistent fashion. Measurement allows objects or events to be compared mathematically either one to another or to an established criterion.
An objective measure is an element of the user's behavior that can be directly observed and verified by one or more observers.
Examples of objective measures:
- task completion time (Time on Task)
- learning time
- frequency of errors
A subjective measure is an element of the user's internal experience that is typically assessed with a rating scale.
Examples of subjective measures:
- the degree of frustration or comfort experienced while using a product
- a product's apparent level of complexity
- the degree to which elements of information or functions in a product seem related to one another
Subjective measures are useful for quantifying elements of product usage that cannot be directly measured through objective means.
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