Creating a digital product guided only by your gut feeling is a risky—not so reckless—enterprise. You need the information to make the right choices. That’s why usability metrics are widely used among other data-driven methods to create successful products. It is an excellent tool for assessing the system performance from a user's point of view.
Arounda is an experienced product design agency renowned among Fortune 500 companies worldwide. We design and develop top-notch solutions for our clients with the help of usability metrics. This article describes how to use formulas and questionnaires to identify user experience problems, monitor progress, and provide insights for improving your products.
Why Would You Need to Measure Usability?
So, what are usability metrics used for? Designers adore usability metrics, as they help to boost user engagement and satisfaction. Additionally, usability metrics provide valuable insights into user behavior and determine a product's or service's success.
Furthermore, a solid statistical approach gives ground to evaluate the changes' effectiveness and control the process. It helps to estimate the KPIs of the team and effectively manage the deadlines and budget.
Knowing all the advantages, the main question in measuring usability is not why but how. Let’s have a closer look at the process.
What Should You Measure with Usability Metrics?
Often, specialists doubt which metrics are the best, as there are many approaches and formulas in the market.
One of the predetermined conditions is a sufficient number of users to observe. In most cases, it is five. For some projects, however, the specialists insist on more than twenty. However, more studies require more time, effort, and expenses.
The usability metrics example criteria include all spheres of the interaction with a product:
- Learnability: How easy is it for users to accomplish basic tasks?
- Efficiency: How quickly can the users perform tasks?
- Memorability: How easily can the users reestablish proficiency after the break?
- Errors: How many errors do users make? How severe are these errors?
- Satisfaction: How pleasant is it to use the design?
To answer these questions, qualitative and quantitative methods are applied.
Measuring the Usability Metrics
There are many usability metrics, so choosing the most relevant to your product or service is crucial. Here are some tips for selecting the right usability metrics for your project:
- Identify Your Goals: What do you want to measure? What do you want to improve?
- Understand Your Users: What are their needs? What are their pain points?
Only then can you decide on the metrics type, analyze, and assess the changes.
Below, we describe the top five metrics which perfectly align with any company and would aid your business development.
Completion Rate
What is usability metrics in terms of success?
The completion rate is one of the fundamental examples of usability metrics to measure success. Moreover, it is easy to use, as there are only two alternatives: whether the user completed a task or not. Here is a formula:
Let’s consider a practical example. The five users were performing a task. At the end of the test session, three users achieved the task goal while the others didn’t. In this case, the overall user effectiveness should be calculated as follows:
Effectiveness=⅗*100%=60%.
Theoretically, one should always aim for a completion rate of 100%. However, according to some studies, the average task completion rate is, in practice, 78%. The higher it is, the better.
Error Rate
The number of errors counts not the completed tasks but the number of errors in the process.
What is usability metrics error? The errors could occur in various forms, in particular, unintended actions, slips, mistakes, omissions, etc. To achieve reliable data, each error should be fully described, rated, and classified under the respective category.
For example, slips are mistakes made with the correct intention, such as spelling. In contrast, mistakes with incorrect intention concern entering the current date instead of the birthdate.
Usually, this type of usability metrics is calculated by counting all errors or by one type (error occurrence rate).
The error rate indicates the overall performance compared to the total number of errors of various types.
Thus, the error rate = the total number of errors / the total number of attempts.
The error occurrence rate shows how often a particular error occurs. It is calculated with the total number of errors of a specific type divided by the total number of attempts.
For example, five out of 100 users failed to type their correct e-mail address in the corresponding field. The error occurrence rate is calculated like this: 5/100 = 5%.
Statistically, the average number of errors per task is 0.7. Only about 10% of the tasks are completed with no mistakes.
Time-Based Efficiency
How do you measure usability for the time the user takes to accomplish the task? Here is the formula. At first sight, it is complex, but a practical usability metrics example will clarify things.
Where:
Suppose four users are performing the same task. Three users complete it, taking 1, 2, and 3 seconds respectively. The fourth user takes 6 seconds and then gives up without completing the task.
Taking the above equation:
N = The total number of tasks = 1
R = The number of users = 4
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It is important to note that time-based efficiency does not consider other factors besides the time it takes to produce the output. Factors such as quality and cost need to be considered to get a more accurate measure of efficiency.
Overall Relative Efficiency
Overall relative efficiency is a type of usability metrics determined by comparing the number of users who finished the task successfully to the overall time for all users. As a formula, it can be represented as follows:
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In the same conditions as in the example above, the calculations will look as follows:
This method is suitable for comparing usability before and after a redesign. It determines whether the changes were successful.
User Satisfaction
User satisfaction is a vital qualitative usability metric. It shows how pleased users are with a product through standardized satisfaction questionnaires.
After users attempt a task, they should immediately be given a questionnaire to measure how difficult it was. For this purpose, there are the following questionnaires.
Examples of usability metrics
To Sum Up
Using usability metrics is a great way to see a design's effectiveness. You can understand if your design is enjoyable or not and change that. You can also use metrics to measure how often people engage with the design versus how often they abandon it.
To this extent, a variety of formulas and questionnaires are used. How is usability measured? In Arounda, we know how to avoid problems with usability metrics and apply the best practices. Our specialists in UX and UI design use the most effective methods to get honest feedback from the users.
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