What is a usability expert review?

With a usability expert review, an evaluator uses a product or web site and assesses its usability against a set of principles or best practice guidelines. Expert reviews are popular because they are much quicker and cheaper to carry out than a usability test.

Jakob Nielsen's ten usability heuristics

Most usability evaluators use the set of heuristics developed 17 years ago by Rolf Molich and Jakob Nielsen. Before this work, lots of people had derived guidelines and principles for usability but there were often so many guidelines that an expert review could take many days to complete. (For example, Smith and Mosier's Guidelines For Designing User Interface Software has 944 guidelines and remains the largest collection of publicly available user interface guidelines in existence.)

Molich and Nielsen's ten guidelines are as follows.

Visibility of system status
The system should always keep users informed about what is going on, through appropriate feedback within reasonable time.
Match between system and the real world
The system should speak the users' language, with words, phrases and concepts familiar to the user, rather than system-oriented terms. Follow real-world conventions, making information appear in a natural and logical order.
User control and freedom
Users often choose system functions by mistake and will need a clearly marked "emergency exit" to leave the unwanted state without having to go through an extended dialogue. Support undo and redo.
Consistency and standards
Users should not have to wonder whether different words, situations, or actions mean the same thing. Follow platform conventions.
Error prevention
Even better than good error messages is a careful design which prevents a problem from occurring in the first place.
Recognition rather than recall
Make objects, actions, and options visible. The user should not have to remember information from one part of the dialogue to another. Instructions for use of the system should be visible or easily retrievable whenever appropriate.
Flexibility and efficiency of use
Accelerators - unseen by the novice user - may often speed up the interaction for the expert user such that the system can cater to both inexperienced and experienced users. Allow users to tailor frequent actions.
Aesthetic and minimalist design
Dialogues should not contain information which is irrelevant or rarely needed. Every extra unit of information in a dialogue competes with the relevant units of information and diminishes their relative visibility.
Help users recognise, diagnose, and recover from errors
Error messages should be expressed in plain language (no codes), precisely indicate the problem, and constructively suggest a solution.
Help and documentation
Even though it is better if the system can be used without documentation, it may be necessary to provide help and documentation. Any such information should be easy to search, focused on the user's task, list concrete steps to be carried out, and not be too large.

Limitations of Nielsen's usability heuristics

But what Mohlich and Nielsen's guidelines gained in brevity they lost in accuracy. Smith and Mosier's guidelines were reviewed by dozens of professionals and based on scores of research papers. Mohlich and Nielsen's guidelines were derived from a database of 249 usability problems from evaluations of 11 interactive systems. As Bob Bailey has pointed out:

“These heuristics, which are widely used, have never been validated. There is no evidence that by applying these heuristics in the design and development of user interfaces that it will improve the interface.”

What alternatives exist? Most usability professionals have their own favourite sets of guidelines or checklists but these suffer from the same problem: they are not research-based but are often a matter of opinion. As a consequence, they are subject to the biases and whims of the reviewer. What we need is a set of guidelines that are based on research and have some international consensus.

Alternative usability heuristics in ISO 9241

International standards meet these criteria. BS EN-ISO 9241-110: Ergonomics of human system interaction - Part 110: Dialogue principles, contains a set of alternative heuristics. These heuristics are based on research and have the benefit of international consensus. The principles, and their definition in the standard, are as follows:

Is the dialogue suitable for the user's task and skill level? (Suitability for the task)
“A dialogue is suitable for a task when it supports the user in the effective and efficient completion of the task. In a dialogue which is suitable for the task, the user is enabled to focus on the task itself rather than the technology chosen to perform that task.”
Does the dialogue make it clear what the user should do next? (Self-descriptiveness)
“A dialogue is self-descriptive to the extent that at any time it is obvious to the users which dialogue they are in, where they are within the dialogue, which actions can be taken and how they can be performed.”
Is the dialogue consistent? (Conformity with user expectations)
“A dialogue conforms with user expectations if it corresponds to predictable contextual needs of the user and to commonly accepted conventions.”
Does the dialogue support learning? (Suitability for learning)
“A dialogue is suitable for learning when it supports and guides the user in learning to use the system.”
Can the user control the pace and sequence of the interaction? (Controllability)
“A dialogue is controllable when the user is able to initiate and control the direction and pace of the interaction until the point at which the goal has been met.”
Is the dialogue forgiving? (Error tolerance)
“A dialogue is error-tolerant if, despite evident errors in input, the intended result may be achieved with either no or minimal corrective action by the user. Error tolerance is achieved by means of damage control, error correction, or error management to cope with errors that occur.”
Can the dialogue be customised to suit the user? (Suitability for individualisation)
“A dialogue is capable of individualization when users can modify interaction and presentation of information to suit their individual capabilities and needs.”

In our experience, developers are more likely to fix an issue with a user interface when we point to an international standard than when we base our judgement on personal opinion. So next time you're reviewing a user interface, try out these seven guidelines. They may not be as well known, but they do have the authority and credibility of an international standard.

About the author

David Travis

Dr. David Travis (@userfocus) has been carrying out ethnographic field research and running product usability tests since 1989. He has published three books on user experience including Think Like a UX Researcher. If you like his articles, you might enjoy his free online user experience course.

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This article is tagged expert review, heuristic evaluation, ISO 9241, standards.

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David Travis Dr. David Travis (@userfocus) has been carrying out ethnographic field research and running product usability tests since 1989. He has published three books on user experience including Think Like a UX Researcher.

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