Usability

Usability is how easy and convenient it is for people to use a site, an app or any interface to reach their goal. The ISO 9241-11 standard defines usability as 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.

In plain words

Usability answers the question: "Can an ordinary person quickly and without errors do on the site what they came to do?" For an online store this means: find a product, understand whether it fits, add it to the cart, choose Nova Poshta delivery, pay or place a cash on delivery order, and not get annoyed along the way.

Jakob Nielsen (Nielsen Norman Group) calls usability a "quality attribute" that assesses how easy an interface is to use. The same word is also used for the methods that improve this ease during design (NN/g, Usability 101).

For e-commerce Nielsen states a simple rule: if users cannot find the product, they cannot buy it. People do not study a complicated site; they simply leave.

The ISO 9241-11 definition: three components

The international standard ISO 9241-11 describes usability through three dimensions (W3C WAI):

• Effectiveness: whether the person reaches the goal at all and how accurately. For example: did the customer place an order with the right product, size and Nova Poshta branch.
• Efficiency: how many resources (time, effort, clicks) it took. An order can be placed in 2 minutes or in 15.
• Satisfaction: how the person feels during and after use: was it pleasant, or annoying. Satisfaction is often measured with the System Usability Scale (SUS) questionnaire (Wikipedia, ISO 9241).

An important part of the definition is "specified users" and "specified context". The same site can be convenient for a 30-year-old manager with a laptop and inconvenient for a person ordering from a smartphone in a minibus with one hand. W3C points out that if "specified users" include people with disabilities and the context includes assistive technologies, usability overlaps with accessibility.

Nielsen's five quality components

Nielsen Norman Group breaks usability into five components (NN/g):

1. Learnability: how easy it is to perform basic tasks the first time the person sees the design. Will a new visitor understand where the catalog is and how the filter works?
2. Efficiency: how quickly the person performs tasks once they have learned the design. Can a regular customer repeat an order in a few clicks?
3. Memorability: how easily the person regains proficiency after a break. A customer who visits once every six months should not have to learn from scratch.
4. Errors: how many errors people make, how severe they are and how easily they can be fixed. For example, a wrongly entered phone number: does the form highlight the error right away and keep the other fields?
5. Satisfaction: how pleasant the design is to use.

Nielsen separately distinguishes usability from utility: whether the product has the functions people need. A site can be simple but lack needed information (for example, a size chart), and then it is useless. Utility together with usability gives usefulness.

How different sources see it

• ISO 9241-11 gives three dimensions (effectiveness, efficiency, satisfaction) and stresses context: usability does not exist "in general", only for specific people, goals and conditions.
• Nielsen Norman Group proposes five components. They are more detailed: learnability, memorability and errors are singled out, that is, how a person learns and makes mistakes over time.
• Interaction Design Foundation names five elements slightly differently: effectiveness, efficiency, engagement, error tolerance and ease of learning (IxDF, Usability).
• Baymard Institute works with e-commerce more concretely: instead of general principles they give over 700 specific recommendations for store pages (homepage, catalog, search, product page, cart and checkout, mobile version) based on tests with over 18,000 users (Baymard Research).

These approaches do not contradict each other. ISO says what to measure, Nielsen says which qualities make up ease of use, Baymard says what exactly to do on store pages.

How usability is measured

Usability testing. The main method: real (or realistic) users perform realistic tasks while a researcher observes where they succeed and where they do not. Users are not helped, because hints spoil the result (NN/g). Testing can be qualitative (find problems) or quantitative (collect metrics), in person or remote (NN/g, Usability Testing 101).

How many people are needed. Nielsen calculates that five users find about 85% of the problems: the model assumes one user uncovers roughly 31% of the problems. Instead of one big test he advises several small rounds of 5 people with fixes in between. If the audience consists of very different groups, each is tested separately, 3-4 people per group (NN/g).

Metrics. - Task success rate: the share of participants who completed the task. NN/g advises distinguishing levels: full success, success with a minor problem, success with a major problem, failure, and not averaging them into scores (NN/g, Success Rate). - Task time and number of errors, to measure efficiency. - Satisfaction: questionnaires like SUS.

Expert review. A cheaper way to find likely problems without participants is a heuristic evaluation against Nielsen's heuristics. It does not replace testing with people.

What does not work. NN/g considers focus groups a poor way to assess usability: what matters is what people do, not what they say.

Online store usability

For a store, usability is directly tied to money, because every inconvenience is one more reason to close the tab.

A few facts from Baymard Institute research:

• The average documented cart abandonment rate is 70.22% (average across 50 studies). Among the reasons: 18% of customers left because the site required creating an account, 17% because of a checkout that was too long or complicated, 17% because of site errors (Baymard).
• By Baymard's estimate, the average large online store can raise conversion by 35.26% through better checkout design alone (same source).
• The average checkout has 11.3 form fields (2024), although most sites need only 8. The average length is 5.1 steps. 42% of test participants at least once typed their full name into the "First name" field when the name is split into two fields (Baymard).

What this means in practice for a Ukrainian store:

• The mobile version is the main one for many stores, so testing must be done on a smartphone first.
• Delivery. Choosing the city and Nova Poshta branch with autosuggest instead of a long list is a matter of effectiveness and errors.
• Payment. Cash on delivery, card payment, Apple Pay/Google Pay: the person must immediately see which methods exist and how much delivery costs. Unexpected extra costs are the most common cause of abandoned carts in Baymard's data (40%).
• Checkout without registration. Forced account creation is a separate reason for drop-off.
• Search and filters. If a product cannot be found, it cannot be bought.
• Comparison with marketplaces. Customers are used to Rozetka and Prom, so a strong departure from familiar patterns (where the cart is, how the filter works) increases the burden; this is directly about the "consistency and standards" heuristic.

How to improve usability

1. Start by testing the current site: give 5 people from your audience real tasks ("find size 42 sneakers under 3,000 UAH and set up delivery to a branch").
2. Run a heuristic evaluation to collect the obvious problems before the test.
3. Fix the most serious ones (see the severity scale in the article on heuristic evaluation).
4. Test again. NN/g advises doing usability work at every stage, from the old design to the prototype and the finished product: structural problems are very expensive to fix after launch.

NN/g gives a guideline: spend about 10% of a design project's budget on usability. According to their data, for websites this on average more than doubled quality metrics (NN/g).

Common mistakes

• Confusing usability with beauty. A beautiful design can be inconvenient, and vice versa.
• Asking instead of observing. "Is it convenient for you?" gets a polite answer, not the truth.
• Testing on colleagues. They know the site and are not like customers.
• One big test instead of several small ones. After fixes you must check whether new problems appeared.
• Testing only on desktop when most customers come from smartphones.
• Ignoring context. A site that is convenient on fast Wi-Fi may be inconvenient on slow mobile internet.

FAQ

What is usability in plain words? It is ease of use: how easily a person can reach a goal on a site, quickly, without errors and without irritation.

How does usability differ from UX? Usability is the quality of the interface. UX is broader: the whole experience of a person's interaction with a company, its services and products, including delivery and support (NN/g).

What are the principles of usability? The best-known set is Nielsen's 10 heuristics: visibility of system status, match with the real world, user control, consistency, error prevention and others.

How do I check the usability of an online store site? Run a usability test with 5 representatives of your audience on real tasks (find a product, place an order) and supplement it with a heuristic evaluation.

How do I improve a site's usability? Find the problems with a test or an expert review, prioritize them by severity, fix them, check again, and repeat the cycle.

Related terms

• UX and UI: what they are and how they differ
• 10 Usability Heuristics of Jacob Nielsen for E-commerce: How to Increase Conversion
• Heuristic evaluation (expert review)
• Customer Journey Map

Sources

• Nielsen J. Usability 101: Introduction to Usability. Nielsen Norman Group — nngroup.com/articles/usability-101-introduction-to-usability
• W3C WAI. Accessibility, Usability, and Inclusion (цитата визначення ISO 9241-11) — w3.org/WAI/fundamentals/accessibility-usability-inclusion
• Wikipedia. ISO 9241 — en.wikipedia.org/wiki/ISO_9241
• Interaction Design Foundation. Usability — ixdf.org/literature/topics/usability
• Nielsen J. Why You Only Need to Test with 5 Users. NN/g — nngroup.com/articles/why-you-only-need-to-test-with-5-users
• Moran K. Usability Testing 101. NN/g — nngroup.com/articles/usability-testing-101
• Nielsen J., Budiu R. Success Rate: The Simplest Usability Metric. NN/g — nngroup.com/articles/success-rate-the-simplest-usability-metric
• Baymard Institute. Cart Abandonment Rate Statistics — baymard.com/lists/cart-abandonment-rate
• Baymard Institute. Checkout Flow Average Form Fields — baymard.com/blog/checkout-flow-average-form-fields
• Baymard Institute. Research — baymard.com/research
• Norman D., Nielsen J. The Definition of User Experience (UX). NN/g — nngroup.com/articles/definition-user-experience