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Usability is defined by the quality of the user experience (UX) when it comes to confident using a product or a system. This includes the usability of websites, software, hardware, applications, or mobile devices. The end goal of usability is to effectively and efficiently satisfy the user.

In this article, System Usability Scale In UX Research, we will discuss further usability and how this is measured using the System Usability Scale (SUS).

What is the System Usability Scale (S U S)?

You may wonder what is SUS and how it matters to UX. The SUS is a 10-item Likert Scale questionnaire that quickly and effectively evaluates the usability of products and designs. This is a practical and reliable process of measuring the usability or ease of use of digital products and services to help UX designers determine if there is an overall problem with the design.

The system was created by John Brooke in 1986, which initially measured the usability of electronic office systems. Fast forward to this day, the System Usability Scale is now widely applied to found the various functions of web-based and technology-based applications to measure how easy or difficult they are to use in order to improve.

User-focused designs help UX professionals prioritize user experience to make the end-product as usable as possible. Having said this, user testing is employed over the course of product development to help make usability improvements to benefit the end-user. And one of the forms of user testing that UX designers employ is the SUS.

How do you measure usability?

Unlike the usability report, the System Usability Scale is not diagnostic and is used to provide an overall usability assessment measures, which is made up of the following characteristics:

  • Efficiency: How fast someone can use it
  • Intuitiveness: How effortlessly someone can understand it
  • Ease: How easy to use
  • Satisfaction: How much a user subjectively would like to use or dislike to use it

System Usability Score Questions

This consists of 10 questions that can be answered on a five-point Likert scale of "Strongly Disagree" to "Strongly Agree."

After each usability testing session, the users are given the 10 SUS questions to complete. These questions are designed to get quick and unfiltered feedback from the user for each testing session and to be answered quickly without interaction from others, including the UX team.

So it is a good practice to use a good working title and description when distributing the questionnaire to the participants to avoid bias or confusion.

You can collect a minimum of 5 user feedbacks for reliable data. The participants are given 1 to 2 minutes to complete the 10 questions. And remember that SUS is only composed of 10 questions that are answerable by the 5-point Likert Scale. This means there should be no further feedback to be collected other than the ranking scores. This will ensure the integrity of the SUS questionnaire.

How do you score the System Usability Scale?

Here’s an overview of how you calculate the SUS score:

The participants will have ranked each of the 10 questions from 1 to 5, based on the level of agreement:

  • For odd questions: subtract one from the user score.
  • For even-numbered questions: subtract the value from 5
  • This scales all values from 0 to 4 (with four being the most positive response).
  • Add up the converted responses for each user and multiply that total by 2.5. This converts the range of possible values from 0 to 100 instead of from 0 to 40.

What is a good SUS score?

The average Systems Usability Scale is 68 based on 500 studies. Above the 68 mark would be considered above average and anything below 68 mark is below average.

The best way to interpret your SUS is to convert it to a percentile rank through a process called normalizing, which is similar to “grading on a curve” based on the distribution of all scores.

The SUS score result is NOT a percentage, but it is a clear way of seeing your score. However, when communicating these scores to stakeholders, it’s best to convert the original score into a percentile so they can easily check if the result is above or below the average score.

The Advantages of System Usability Scale

Compared to other tests, the System Usability Scales is:

Reliable

SUS has shown more reliability at smaller sample sizes compared to home-grown questionnaires and other commercially available ones. Sample size and reliability are not correlated, and thus, SUS can be used on very small sample sizes (which is possible to even two users) and still generates reliable results.

But take note that a small sample size generates imprecise estimates of the unknown user-population SUS score. Thus, you need to compute a confidence interval around your sample result to understand the variability in your estimate.

Also used to measure both usability and Learnability

We know that SUS is created to measure the ease of use, however, some researches show it also provides a global measure of system satisfaction of usability and learnability.

Valid

SUS has been shown to efficiently recognize between unusable and usable systems. It also correlates highly with questionnaire-based measurements of usability.

Cheaper

A 10-item questionnaire does not require a lot of resources to administer. This test is very cost-efficient and is perfect for those who are constrained by budget.

Quick

There are so many SUS templates readily available, so all the hard work has been done for you.

Best Practices for Incorporating the SUS into Usability Testing

When administering SUS to participants

When it comes to confident using standardize questionnaires like System Usability Scale, UX researchers should carefully administer the test to achieve the satisfaction of outcomes.

This means that UX researchers should consider proper time in testing and as well as provide clear and exact instructions to their participants to measure user satisfaction accurately.

It is best to conduct System Usability Scale SUS as soon as the participants have completed all tasks. This will help the participants remember everything and thus, provide you with accurate answers.

When administering a series of identical tasks to participants

When you would like to use identical tasks to compare two or more products, these tasks may become easier as they are repeated. This may lead to higher SUS scores as well, regardless of how usable it is. So to avoid such a situation, UX researcher should alternate the order of tools to be tested from one participant to the next when it comes to testing multiple products or systems.

When understanding the participant’s user experience

UX researchers should also consider the participant’s user experience or prior use of a product or system since this can impact scores when using SUS-like questionnaires Most likely, prior experience leads to higher SUS when compared to participants with less or no experience at all. Researchers should recruit more participants with no or limited experience since familiarity and experience can lead to higher SUS scores.

Final thoughts

In this article, we have learned that SUS is a quick, easy to use, and reliable way of assessing the ease of use of the design. This test, however, does not provide insights to specific problems, but rather provides easy feedback on the overall ease-of-use of a website, application, or solution from a user’s perspective.

As UX researchers and designers, never be satisfied by getting a good SUS score when performing a UX study. The only way to achieve a well-designed, user-friendly product is to get going with user research by keeping up with how people would perceive the product or people would learn the product based on their changing contexts, and continually could get going with evaluation, adjustments, and improvements of the end-user design .

Mary Ann Dalangin

About the author

A content marketing strategist and a UX writer with years of experience in the digital marketing industry.

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