The Term “Usability” is Confusing

As user experience people, we often use the words that describe what we do casually or imprecisely. This confuses people who don't eat, sleep and breathe usability.  I know people who say “I do usability” or “I need some usability testing.”  What they’re really saying is “I specialize in making things more usable” and “I have to figure out what’s wrong with this application and fix it so my customers can complete their orders.”

Sometimes people talk about usability as a process – doing “usability testing.”   Sometimes it is described as an attribute of an artifact – “that application is really usable.”  Both are reasonable, but the difference can be confusing. 

Usability as an Attribute

We can often say that one system has greater usability than another system based on measurements of user performance measures.  In aggregate, these measures constitute an overall usability attribute that describes how easily people can use the system to achieve a goal.  Usability as defined by NIST and others consists of three measurable components:

• Efficiency - can people work quickly with the system?
• Effectiveness - can people work easily without errors?
• Satisfaction - is their blood pressure higher or lower after using it (or, more practically, how do they rate their experience)?

For instance, we can measure how many transactions happen in a given period of time or the number of errors that are made.  Ultimately, the results of these measurements are interactions between design factors and properties of the user.  Measurement leads to diagnosis; diagnosis leads to interventions that, in turn, we hope, increase the usability of the system.

Usability as a Process

On the other hand, we also use the term “usability” as an adjective to describe a process, such as “usability engineering” or “usability testing.”  Having a usable system is the end point in the usability engineering process.  It is more of a journey, and relies on understanding the science base of human factors and engineering psychology, user interface standards and guidelines, and research tools from behavioral sciences. 

Knowing what needs to be changed does not mean we know how to change it to improve the design.  For that we need designers skilled in the art and science of user experience design.  Highly usable systems derive from a usability process that relies on:

1. Understanding and respecting users, tasks and environments.
2. Setting user performance/satisfaction objectives.
3. Designing a user interface that meets those needs.
4. Testing how well the tool meets the needs.
5. Iterating the design and test until performance objectives are met.

Usability is not a difficult concept, but sometimes we make it confusing.  Perhaps we need better terms.