Usability

“Usability is a quality attribute that assesses how easy user interfaces are to use. The word “usability” also refers to methods for improving ease-of-use during the design process.”
(Nielsen, J. (2012) Usability 101: Introduction to Usability. URL: http://www.nngroup.com/articles/usability-101-introduction-to-usability/)

  • Learnability - Can new ysers easly understand how to perform basic tasks?
  • Efficiency - Are returning users able to perform their tasks with good timing?
  • Memorability - How easy is it for users to remember how the system works, even after not using it for a significant amount of time?
  • Errors - How frequently do users incur in errors, and how serious are these? Is it possible to recover from errors?
  • Satisfaction - Is it pleasant to use the design?

Usability can be applied to any type of interface - Such as software applications

Evaluation

Jakob Nielsen, a pioneer in the field, stated that five users are all it typically takes to find most usability problems in an interface.
Testing multiple times allows for constant improvement, this can follow a progression from low-fidelity prototypes to full applications.

Heuristic Evaluation

  • Heuristic
    • Technique based in past exprience that can assist at arriving a solution for a problem
  • Heuristic Evaluation
    • Use of heuristics to determine (and sometimes quantify) quality
    • Informa, but useful mechanism
    • Experts examine an interface and evaluate it against a set of principles

Nielsen’s Usaiblity heuristics

  • Several sets of usability heuristics exist, the most well-known are Nielsen’s

Visibility of System Status

The system should always keep users informed about what is going on, through appropriate feedback within reasonable time

Match begin system and the real world

The system should use words, phrases and concepts familiar to the user - rather than system-oriented terms
It should follow real-world conventions, making information appear in a natural and logical order (like the floppy disk save button)

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 dialog
Software should support undo and redo functions

Consistency and Standards

Users should not have to wonder whether different words, situations, or actions mean the same thing
Follow platform conventions

Error Prevention

A better solution to good error messages is to prevent the error from occuring in the first place!
It is important to eliminate error-prone conditions or at least check for them and present users with a confirmation option.

Recognition rather than recall

Users should be able to recognise objects, actions and options rather than have to remember them.
Users should not have to remember information from one dialog to another.
Instructions for use of the system should be visible or easily retrievable whenever appropriate.

Flexibility and Efficiency of Use

Accelerators may often speed up the interaction for expert users (alt-shortcuts in Office)
Allow users to tailor frequent actions

Aesthetic and Minimalist Design

Redundant, irrelevant and rarely needed information should not be presented
Every extra unit of information in a adialog 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

It may be necessary to provide some help and documentation even for an intuitive system
Any such information should be easy to search, focussed on the user’s task, list concrete steps to be carried out, and not be too large