Campbell, who has more than 10 years' experience in user interface design with companies including IBM and Barclays Bank, backed up her point with an account of a serious problem with an Internet shopping site run by a leading UK retailer, which she declined to name.
Ninety per cent of customers who had placed products in their Internet shopping baskets logged off the site before making a purchase, the retailer found.
Bemused and frustrated, the company conducted 20 focus groups with 12 people each in an attempt to find the root of the problem. Only after extensive research did they discover that shoppers were typing in their credit card numbers according to the four-digit clusters as they appear on the card, with spaces between each cluster.
E-commerce software rejected the numbers typed in this way and told shoppers that there was a problem with the credit card.
Once the retailer amended the problem there was a sharp rise in Internet trade, Campbell said.
Interface experts like Campbell recommend hands-on testing of prototype mock-ups of e-commerce software before it is built.
Even dummies made from cardboard and paper could flag up potential difficulties before the expensive process of software development is started, Campbell said. She warned that simply surveying the public on what they liked about technology only provided "preference data", limited in its value.
When people are surveyed about their technology likes they tend to ask for everything - but what people ask for is not necessarily what they will use, she said.