Most people in IT know that usability has "something" to do with user friendliness or ease of use. But what exactly is that "something"? And more importantly, how can we make this tangible and testable?
ISO uses the following definition of usability:
"The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use."
Lets examine this definition to find out what it means.
The properties of usability
Usability is a quality attribute by which certain characteristics of a product, the test object, can be qualified and assessed. This is illustrated by the following example. Have a look at the following three hammers:
Which of these three hammers has the best usability?
At first sight an opinion is readily made. Many people choose hammer C because this is the most common hammer is to hit nails into a piece of wood. But that statement includes an unconscious assumption: that a user has the task to hit a nail with the hammer. Hammer A has many other functions and thus is not exactly the most convenient tool to hit a nail. But if you have to uncork a bottle this hammer is by far the best. So, for the determination of the usability is the goal is important. What do you want to achieve with the tool?
Different users have different requirements for tools. One user hammers better with a heavy hammer, the other with a light one. One user could has preference for a hammer with many features like A, another likes a simple hammer like C.
Before we can make decide on the usability of a test object more things are important than just the properties of the test object and the purpose for which it was designed. Therefore in the definition of usability it is stated: Usability is the degree to which a product can be used by particular users in a particular user environment ... The user is the person who determines the goal and is also the one who has to use the test object. In addition, the user environment or situation is important here.
This interdependence of situation, task, test object, purpose and user sometimes makes it difficult to make general statements about usability. Everyone has different preferences and what works for one user, does not work for the other. This can be resolved by looking at user segments: has the object a particular usability for users with certain similar characteristics?
Fortunately, it is also often the case that indeed a general statement about usability can be made. In our example, Hammer B is made of chocolate; useless to hit nails with.
How to measure usability?
Having established that usability makes a statement about how the application is used by a user to achieve a specific goal, the usability of an object can be determined and this can be communicated.
There is still terminology needed in order to indicate whether the usability of a product is good or bad, it is high or low. This requires a more objective, specific and measurable way to describe usability. This mode of expression should also facilitate in performing tests and checks. The second part of the definition of usability presents the required terminology ... to achieve certain goals effectively, efficiently and satisfactorily.
Efficiency indicates a certain degree of productivity. "User X hits with hammer Y 15 nails per minute." Effectiveness indicates a certain degree of results "User X hits 7 out of 8 nails with hammer Y well." Satisfaction can be made specific and measurable in another way: "User X indicates that he is satisfied with the use of hammer Y. He rates the use at 7 on a scale of 10".
These terms allow us to formulate the usability of a product assessed more precisely. The terms also allow us to communicate at a high level about usability and to create specific usability requirements. They make it measurable. They enable us to make agreements about usability with the client.
What ways are there to test usability?
So the next step is to start testing usability. There are many ways and techniques to do this. One way to start is to visit the new Usability testing Building block from this site.
Thomas Veltman is a senior test consultant