Understanding the determinants of usability beyond http

Introduction

"[Usability refers to] 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 user."
-- ISO 9241-11 ^[1]

Usability is a subjective measure of how well a system helps the user achieve their goals in the environment it will be used. The phrase above is a much more general and much better description of what usability is then most other definitions easily available on the net. Usability information on the internet often concentrates solely on the usability and interface design of web sites and web applications. This is ironic considering the prolific Technicolor web sites which litter FaceBook and MySpace, two very popular social networking sites.^[2]

Discussion about usability often ends up focussing on interface design. Most discussions ignore the importance of system performance, function and form. It is important to note that in this instance system is not necessarily a computer system but any single entity from a kitchen oven to the space shuttle.

This article is separated in two parts. Firstly I will discuss the relative importance of internal factors interface, performance, function and form as a determinant of usability. Secondly I will look at external factors like environment, user experience and user attitude as modifiers to the perceived and actual usability of a system.

I will use individual examples to illustrate my points but it is important to remember that when we talk about usability in general it extends far beyond the web accessibility and usability that it now commonly refers to. The fundamentals of achieving good usability remain consistent no matter what type of system we are discussing.

Defining usability

The interface

Jakob Nielsen is an internationally recognised author on user interfaces specialising in web site interface design. In 1994, well before the popularisation of the internet, Nielsen defined a set of heuristics which form some principal rules of thumb for user interface design.

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. Either eliminate error-prone conditions or check for them and present users with a confirmation option before they commit to the action.
Recognition rather than recall	Minimize the user's memory load by making 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 recognize, 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

Reproduced from useit.com^[3]

Each of these ten points serves to reinforce the most important part heuristic of them all: Recognition rather then recall. Making sure users can recognise what to do rather then forcing them to memorise how to use a system is a very important aspect of interface design. It would quickly become overwhelming if your every day appliances like cooker, radio and television required you to learn how to use them each time you wanted to use them.

The example above illustrates how three of the rules above blend together to make the operation of a DVD player intuitive to most people. When we look around the home we find that many every day items include similar standardisations which we no longer think about. The symbol for power on/off symbol, grill, volume and even a simple electrical socket switch has been standardised so much that it has become second nature for people to interpret and interact with them.

Performance, Function and Form - the unknown three

It is undisputed that the design of a user interface plays a major part in the evaluation of system usability. A quick search on the internet would suggest it is the only determining factor of usability. While it is certainly the factor that receives the most public attention, especially with the recent launch of Microsoft Windows Vista, I would argue that it has three equals which must also be included in any thorough evaluation.

In the second part of this document I will discuss the human and situational factors which impact on the perceived usability of a system and as such erode the seemingly overwhelming importance of the user interface.

Buying a car is one of the biggest financial commitments a person can make and it is done almost exclusively based on performance. Whether the user evaluates performance as top speed, acceleration, petrol efficiency or any other factor the performance of the vehicle plays the single biggest role in the decision making process for most people.^[4]

I would argue that most people would not discount buying a vehicle if they were not overly impressed with the way the CD player worked. People will refuse to buy a car which is not comfortable or does not meet their needs on another level including practicality or performance.

This leads us to conclude that function is another major factor in determining overall usability of a system. The system must fulfil the requirements of the user, or at the very least make it clear what the limits of the appliance are.

Finally form plays an increasingly large role in a society where personalisation, customisation and individuality play increasing roles in our daily life. The advent of interchangeable phone covers accelerated the growth of an industry centred on allowing people to express themselves in their own way. Now these trends have expanded beyond the humble mobile phone. Laptop manufacturer Dell offering interchangeable laptop colours, Apple produces music players in a variety of colours and third party manufacturers complete the colour spectrum with countless coloured cases for all occasions.

Form, otherwise known as product design, now plays a huge part in the decision of users where to spend their time and money. This is particularly prevalent with the younger generations where style is king. Style continues to play a big part in the decisions of consumers when making purchases, even big purchases like cars and property are heavily influenced by the immediate appeal of the product. Good form is often what will initiate the user interaction and will lead them to experience the other determining factors of usability.

Some may argue that form does not have any impact on usability of a product. If we reflect on the quote from the ISO definition "achieve specified goals with effectiveness, efficiency and satisfaction" we notice that projecting class, status or wealth can be a goal which the user wishes to achieve and falls within the definition.

Summary

Usability is an important factor during the development and production of systems. For most products the potential customer has many alternate choices and the interaction experience a user has with a product will either bolster or taint the perception of the product and brand in the eyes of the consumer. This could potentially earn or cost the company huge sums of money in the future.

In this section I have discussed the four pillars of usability: interface design, performance, functionality and form. I have illustrated how each of these effects a user's perception of a system and why I believe they are important determining factors.

Beyond the system

Up to now I have discussed what I will refer to as internal factors which are built into each system. The company is able to change internal factors if it decides to do that. I believe there is a second set of external factors which also influence the usability of a system. Companies will take these into account when building their systems but do not have direct control over them.

In this section I will discuss the three major external factors which I have identified, environment, users' experience and user attitude. I will show how these factors supports my original claim that usability is a subjective measure and show that these factors are indeed determinants of usability.

The expected environment in which the system is to be used plays a major role how the system should be built and acts as a strong modifying force on any proposed user interface. Video playback on the home PC has been around for many years and is usually achieved by using one of the many freely available video players on the market. Navigating the file system to locate the video and playing it is fairly effortless for most users and easily achieved with a mouse and keyboard input.

Recent market advances into the theatre PC has brought the computer into the living room. Suddenly the same actions on the same platform become much harder unless the interface is changed. With old standard definition TVs the resolution does not lend itself to small writing and intricate icons and menus. Software developers have had to redesign the interface to allow users to view details on a TV screen often using a remote control instead of a mouse. By changing the environment the suitability of an interface is changed dramatically.

Virtually all home and office computer systems are now controlled through a graphical user interface with a pointing device and icons. For the home and office users this is mostly a very easy and efficient way of navigating the options within a software application. Users of the computer systems at travel agents have a second system which they use frequently to find travel information (usually flights and trains) based on a text interface. This powerful text based system uses a tightly defined user input schema for searching and printing travel details. If this kind of system was implemented in the home of office for accessing e-mail or browsing the web it would be completely disastrous and fail even the most basic tests set out by Nielsen. Relatively few people have the knowledge or patience to read e-mail through a VI style interface.

The reason this interface has successfully fended off the introduction of the graphical user interface at travel agents is it is a very powerful way to search and obtain information from a very large information pool. For the travel agents using this system day to day it is much faster searching for information using a formatted text string then having to fill in a web form like home users do at Expedia. The users require special training to use the system but with repeat use the advances in speed and efficiency far outweigh the time required to learn the system. This breaks one of the rules of thumb laid down by Nielsen.

Finally the attitude of users plays a big role in the perceived usability of a system. Manufacturers often put extra effort in to making products attractive to certain markets. Mobile phone makers Sagem has a phone specifically designed for the older generation and people without the technical inclination. Their VS4 mobile phone uses larger buttons, simple menus and fewer gimmicks to make the mobile phone accessible to these people.

People naturally resist change; this is especially true of older generations. Radically changing user interfaces like Microsoft has done with Office 2007 is a risky strategy and initially leads to many people claiming the interface is a step backwards in usability ^[5].

An individual's attitude to the system will plays a major part in how much effort they are willing to put in to use the system. While hardcore video gamers will happily spend hours learning intricate input mechanics and control schemes most casual gamers who play on MSN Games look for instant gratification and if the interface design is not immediately obvious they will move on to a different source of entertainment.

Summary

External factors do play a large role in determining the usability of a system. Unlike internal factors the scale and importance of the external factors is difficult to quantify within a given system and an analytic approach like that of UML can not be applied to solve this difficulty. Despite these problems the external factors must not be ignored when evaluating the usability of a system as they make up a key component to determining usability.

Conclusion

Determining usability is a difficult challenge for system developers in all industries and a great deal of time and energy is spent on investigating the usability of existing and new products. Focus Nielsen provides us with a well defined and comprehensive set of rules which helps in the design and analysis process. Interface design is a challenging subject, especially within the software development and web development field both of which are relatively young industries continuously reinventing themselves.

In this article I have tried to expand on the generally accepted defining factors of usability and included factors which I see as important and have offered some proof to support this point of view. By looking at these external factors we can begin to understand why there are so many different interfaces for doing the same thing. ^[6]

References

[1] Usability.gov: Your Guide for developing usable & useful web sites.
http://www.usability.gov

[2] The top ten web design mistakes of 1999
http://www.useit.com/alertbox/990530.html

[3] Jacok Nielsens' Ten Usability Heuristics
http://www.useit.com/papers/heuristic/heuristic_list.html

[4] Times Online Hot to decide what to buy (car guide)
http://driving.timesonline.co.uk/article/0,,13189-1914467,00.html

[5] Office 2007 faces snail's pace migration - The register
http://www.theregister.co.uk/2007/01/23/microsoft_office_2007_uptake/

[6] GUI / Window Managers
http://www.linux.org/apps/all/GUI/Window_Managers.html