[UX] Understanding usability (Definition of the usability)

Jacob Nielson defined Usability is a kind of quality factor to estimate the use of ease for UI. He also defined sub-factors, Learnability, Efficiency, Memorability, Errors, Satisfaction for Usability definition. There are still different definitions like from ISO or other experts.

(Translated in Korean: Link)

In the previous article, I mentioned Usability is one of the success factor for designing a nice UX.

At this posting, I am going to define a concept of Usability that has discussed for a long time. Honestly, the concept of Usability has been talked about since 1990s, and the concept had started to discuss with HCI concept for a long time ago. I meant Usability has been researched for a long time since the concept was defined. (This concept is still hot to people who are interested in UX, no matter what.)

However, Usability has researched by many researchers, so this concept is broaden so much. That's why it's very hard to define specific words for that actually. Defining a concept is always difficult to get out of the subjective opinion when we define it. Especially, many concepts in HCI area are hardly generalized for normal people. I think that's the problem when we research something theoretically.

In other words, for some people, a concept is meaningful but for others are not agreed with that concept though, so I think it's very hard to say which concept is correct or not in every case.

Even if I know this approach is not always correct, I want to define a concept of Usability because I'd just like to let you have the same background conceptually when we work together for UX. If you understand my effort or just agree with what I am saying, I think that's enough to post this article.

1. Jakob Nielson's Usability

According to Jakob Nielson, he is a father of Usability research, Usability is one of the factors when we estimate the quality of UI like how UI can be used easily. He also defined that Usability means a way to improve the product while we are on a progress to use a product or service easily.

He defined Usability with 5 detail concepts below.

a. Learnability(How easy do users feel something new, or how easy do they do tasks basically?)
b. Efficiency(How fast do they do their tasks when they are used to the design?)
c. Memorability(How easily do they do their tasks when they haven't seen the design after they already knew that before?)
d. Errors(How easily do they overcome the errors, and how often do they make some errors with the designed UI?)
e. Satisfaction(How do they feel pleasant while they are using the UI?)

As he defined Usability, he focused on how easily people can do their tasks.

2. ISO(ISO 13407)'s Usability

According to ISO, Usability is a kind of expansion of products, and also that is efficient, effective, satisfying to achieve their purposes on a specific context. For this definition, they defined Usability with 4 detail concepts below.

a. Effectiveness(Completeness,accuracy for achieving user's purposes)
b. Efficiency(Resource that is used when they do their goal completely)
c. Satisfaction(Positive attitude for using the product, and getting out of uncomfortableness)
d. Context of use(Environmental physical characteristic surrounding users and tasks)

3. The other's opinion

Moreover, other researchers have studied Usability, most of all studies are related to make the concept in detail or to classify the concept.

For example, when we design Usability on a product or service, we should consider both objective and subjective points. They defined that objective point can be classified by Effectiveness and Efficiency, and subjective point can be influenced by Cost, Reliability, Safety. Each point desires different goal. Firstly, object point is for doing the task functionally, and the other one is for ease of operation, ease of cognition.

That means they defined that Usability is not only for the functional characteristic but also the aspect on user's side when users do their tasks.

As this approach, Universal usability was made by some researchers, and this concept is used as "Universal Design" though nowadays.

4. Summary

Before I started this article in the body, Usability is hard to be defined by some words, and some concepts of them can't be represented for Usability. (For instance, as learnability is good, that doesn't have a good Usability.)

Anyway, as the concept of usability is evolving, it is hard to explain usability with some objective concepts. I meant we can't differentiate our product with the efficiency and effectiveness of Usability any more, and we are living this era.

As you know, the only function of the product can't make users satisfied any more.

For this reason, the more emphasizing subjective characteristic of the product is more important to give a positive experience to users while we are talking about Usability. For example, Safari, Apple's web browser, is not so good for surfing all web sites that is developed by Active X but some users feel convenient for blocking harmful web site.

Even if this concept is changing, I would like to say to go back to the basic of Usability. I have continuously emphasized this since last article. How many do we miss something basic for Usability, when we just consider some subjective points nowadays?

So far, many UI of products are still inconvenient to users when they do their tasks. (There is a bad example that is not considered by the objective point of Usability functionally.) I want to say that why the products are still inconvenient, and we really have tried to improve it for users while we are designing UI.

I have frequently heard "We had to give up Usability of the product with a limited budget and schedule".

Of course, I can understand it, and I am also thinking about that but it's much more important to know which is good or bad in Usability as an UI expert. (I always want to say to you that it's hard to have braveness to show your fault, and you can improve it when you admit your fault and know it.) Hopefully, you can find the second best solution to solve the problem as much as you can.

You know how many times we have chances to improve it as we are living.