Usability is not an add-on

Steven PembertonCWI, Amsterdam

A thought experiment

What are the features of websites that you go back to regularly that differentiates them from other websites with the same purpose?

Differentiating features

Forrester did some research in this Good content (75%) Usability (66%) Speed (58%) Frequency of updating (54%) (The rest is noise: 14% and lower)

This is surprising

User testing is the first item to go when looking for reduced costs

Many web-building companies have no usability experts on their staff

Many web-building companies build sites that are measurably unusable

What is usability?

It can be summarised by three factors: Efficiency:

how quickly you achieve what you want Effectiveness: how correctly you

achieve it Satisfaction: how much you enjoy doing

it

Compromises

Sometimes these factors have to be balanced out: An experiment with 3 chess-playing

interfaces (command-line, mouse, and real manipulation of chess pieces) showed that the mouse was the fastest

But with real manipulation, the user won more often (was more effective)

Surprises

The psychology of human beings can cause some surprising results: In a test with three methods of writing

(pen on paper, a text editor, a word processor) users wrote less with a pen but of a higher quality, more with a text editor but of a lower quality, and more with a word processor but with a higher quality.

Transparency

A fourth aim of user interfaces is transparency: you don’t notice a good user interface, you spend all your time solving the problem.