1. Usability is not an add-on Steven PembertonCWI, Amsterdam

2. 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?

3. 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)

4. 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

5. 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

6. 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)

7. 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.

8. 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.