Understanding Contextual Usability
Usability is something that users of any mobile app don’t even think about when it’s in, but immediately notice when it’s gone, or use the term coined by the famous psychologist Frederick Herzberg, a hygiene factor.
What do we usually mean by usable? A definition from ISO Standard which states that usability is the extent to which a system, product or service can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use.
Looking closely at the definition, it gathers everything you need: users, their goals, an interactive product or service, the context in which the interaction occurs. The definition is quantitative and distinguishes three component factors of usability Effectiveness, Efficiency, and Satisfaction. The definition combines all metrics into a single judgment. Let’s focus on separate specific usability metrics.
EFFECTIVENESS
usability metrics included in the effectiveness class are related to the achievement of a user’s goals it should be noted that achieving the goal is just as important as the absence of negative consequences which may occur during the goal achievement.
A user should not only achieve the goal but also understand that she has achieved it. Otherwise, she could try to perform this same task again. And we cannot always measure the goal achievement using a binary scale. The binary scale works well only for very simple tasks like checkout in an e-commerce app. For more complex tasks more elaborate measures should be applied. A user goal might be to learn something new. For instance, a lesson in some language learning app. In this case, the effectiveness can be measured by assessing the learning performance using an ordinal scale.
EFFICIENCY
Efficiency metrics are related to the resources expended about the accuracy and completeness with which users achieve goals. The most famous metric of this class is, of course, the time taken to complete a task or set of tasks. But it’s not the only one. You can measure the input rate, that is the number of atomic tasks performed in a certain period, like keystrokes in a typing task; the user’s mental effort when using the interface; deviation from the shortest way to perform a task; learning via changes in task completion over time, etc. Take a look at the quote on this slide. According to JoAnn Hackos and Janice Reddish*
To be usable, an interface must also be perceived as usable by those who must use it or choose to use it. They must be pleased, made comfortable, even amazed by how effectively their goals are supported by your design. In the best case, they will be oblivious to the design — it simply works so well that they don’t notice it. The truly usable interface is transparent to the work the user is trying to accomplish*.
In evaluating usability, it’s crucial to use both subjective and objective metrics. And I’m not talking only about the metrics of the satisfaction class, but also about metrics of the two other classes.
Estimates of effectiveness and efficiency can be derived from opinions that users express about the interaction and its outcome. Subjective assessment by a user of his performance is no less important than objective efficiency metrics such as time on task.
SATISFACTION
According to the ISO standards, satisfaction is the response of users to the interaction with a product. As with effectiveness and efficiency, satisfaction can be assessed using both subjective and objective measures. Objective measurement can include monitoring the psychological responses of a user. The most popular of subjective measurement is the personality test score based on a questionnaire. The quantitative evaluation of usability involves identifying a set of metrics for each user function. Each set consists of usability metrics of all three classes.
What our users consider usable and how designers define usability, is dependent on the context of use. To illustrate this statement using the example of a commonly known virtual keyboard that you use every day if you have a touch-enabled smartphone. Let’s imagine the same person in two different situations.
In the first situation, Mr. X has to write a few numbers, quarterly report amounts, and a short sentence, so Mr. X must compose a message without errors. Perhaps the most significant measure of usability, in this case, is tolerance to errors, but how do we measure them? The right metric here is the number of misprints in the message sent. I’m not saying this is the only metric that virtual keyboard designers ought to use to determine usability, for each user task, we need to define a set of usability metrics. Now let’s imagine Mr. X, who is driving, his partner, who has no idea that he’s driving right now, just asked him an urgent question via Whatsapp. But she won’t call her because the answer to her question is very brief. What’s important for Mr. X here? He drives the car and sends the message in parallel. It is, of course, important to distract yourself as little as possible from the road. The metric presented on this slide takes into account both activities (driving and entering text). It’s quite clear that in this situation the virtual keyboard is not the most usable solution. Mr. X chose to use voice input. Let’s just try and look at all scenarios for a moment. The same human, the same virtual keyboard, the same task and different conditions in the world. As a result, Mr. X considers the keyboard accessible in one case and the other, unusable. Usability is dependent on the context of use.
In summary, usability is the degree to which the program, product or service can be used by specified users to achieve the defined objectives with effectiveness, efficiency, and satisfaction in a particular context of use. How we define usability is dependent on the context of use. It is important not only to consider high-level goals in the sense of usage but also to take into account its other features which can affect the interaction between the user and the application.