The success of a vacuum cleaner that swept all before it highlights the importance to business of effective design. But it's not always easy to quantify, says Hugh Aldersey-Williams
Vacuum cleaner tycoon James Dyson cleaned up at the Design Business Association's sixth Design Effectiveness Awards announced earlier this week. He won the award in the product design category and the event's overall Grand Prix for demonstrating that his design is effective in the best way possible - by sheer overkill.

Dyson makes two "cyclonic" vacuum cleaners, an upright and a cylinder. Both use a high-speed air vortex to deposit dust in a bucket, doing away with the need for the bag that quickly becomes clogged in conventional cleaners. The upright now outsells each of its main rivals, Panasonic, Hoover and Electrolux, by a factor of five. Dyson's cylinder has grabbed two thirds of the premium cylinder market since its introduction in 1995 largely at the expense of the previous market leader Miele. Dyson himself engineered and designed the products and then set up the company to manufacture them.

But it is seldom so clear that design is at the root of success. Last year, Gossard's Utltrabra packaging won an award. But was it the design which was effective or the general awareness of uplift bras created by the rival Wonderbra's advertising and the subsequent PR dream of the tabloids' "bra wars" story?

Such uncertainties favour designs introduced without much advertising or PR - such as Dyson's vacuum cleaner or the 1995 Grand Prix winner, a redirection form for the Royal Mail. The clarified redesign repaid its costs in days thanks to reduced staff time costs.

This year's other winners were strong in own-branded products such as Asda's Pilsner lager and Boots' nicotine patches. But does their success reflect consumers' willingness to trust major retailers more than manufacturers rather than effectiveness of packaging design?

One explanation for the strong showing by own brands may lie with the design strategy of the retailers. Halfords and Waterstone's join Boots and Asda as finalist companies that have established long-term relations with master design consultancies which then co-ordinate work by other designers.

The Hutchison Microtel mobile telephone service, Orange, won in the corporate identity category. It has achieved higher consumer awareness than rivals Cellnet and Vodafone despite being last into the market, thanks to advertising that exploits the strong identity.

Separating the role of design from advertising and external factors remains a challenge. One approach may be to analyse more closely. As part of a Middlesex University MA thesis, David Pilbeam proposes extending the definition of effectiveness to cover aesthetics, sociological and environmental benefits alongside simple manufacturing and market success. A fashion item might score high for aesthetics, an engine part for efficacy.

Pilbeam also edges towards a "grand unified theory" of effectiveness, proposing that clients weight design, advertising and PR on a case-by- case basis. "By evaluating each of these areas and combining them, an overall holistic view of the success of the design project might be arrived at," he says. One difficulty would be to persuade the various creative gurus to agree the extent of their respective contributions. Simple indices of input such as spend or consultancy fees might prove misleading.

But perhaps something is being missed in this emphasis on facts and figures. Despite an abundance of programmes to reward design excellence worldwide, the UK is virtually unique in praising effectiveness. Since the first awards in 1989, only Canada has emulated the DBA's scheme.

There are reasons why Britain is the first country to single out design effectiveness for attention. The scheme is modelled on the long-established effectiveness awards in the advertising industry, the success of which has been the bane of many designers' lives. It is comparatively easy to demonstrate such effectiveness in retail and communications design, areas of British strength. Product assessment takes longer and is harder to prove.

Elsewhere in Europe, there are many prestigious design awards programmes. But none considers effectiveness separately from overall excellence. The "Red Dots" of the Design Zentrum Nordrhein Westfalen in Essen, Germany for example, are given after judgement of many aspects of design - the degree of innovation, ergonomics, environmental impact, and others.

The European Design Prize rewards the overall way companies use design to innovate. (Dyson earlier this month became a national finalist for this award too). But John Thackara, director of the Netherlands Design Institute, one of the organisations that administers the prize, understands the impetus towards more supposedly objective analysis. "The multinationals and bigger companies have recently started to realise how much they spend on design, and it's more than they thought. Now people are saying they have to be able to measure this stuff. So the UK experience will be of interest to people elsewhere in Europe," he says. A poll of European Design Prize finalists revealed that half would like tools to assess design effectiveness.

But Thackara warns that the effectiveness debate is losing touch with reality. No amount of evaluation of past success can guarantee success in the futuren