For agencies, the observation has fuelled the collective insecurity which manifests itself in an almost obsessional mission to convince customers that advertising effectiveness is quantifiable and measurable. For advertisers, it lives on in a fruitless search for perfection - advertising whose effectiveness is totally measurable and, therefore, guaranteed. As Gary Duckworth, the DFGW chairman, points out on page 22, Leverhulme may have led everyone down a blind alley where - in the words of Starcom Motive's Mark Cranmer - advertising is "overmeasured and undervalued".
Overmeasured? Almost certainly. Pressures on budgets are leading many advertisers to demand levels of accountability that are impossible to deliver. Claude Hopkins, one of the founding fathers of US advertising, once declared that if there was a foolproof method of pre-testing ads he could make $1 million a day.
However, he was forced to concede that there was no such thing.
This isn't to say advertising shouldn't strive for effectiveness or to dismiss all attempts to measure it is pseudo scientific tosh. Used badly, it offers dozens of reasons why creative work won't fly and no single reason why it will. Used well and early enough in the process it can be the sparkplug for a long and successful campaign.
Undervalued? That's equally true. Advertising has always defied precise measurement because of its ability to stimulate a range of human emotions - aspiration, a feelgood factor, self-confidence.
The danger is that the harshness of the economic climate is extending the fault line separating agencies and clients. Agencies' raison d'etre is their creative potency and they bridle at the constraints on it; advertisers shy away from allowing creative indulgence with insufficient assurance that it will work. And they're right. You only have to watch a few hours of peaktime TV on any night of the week to see ads that any worthwhile measurement system should have strangled soon after birth.
The important thing is to recognise measurement's limitations. Research by Euro RSCG Worldwide to coincide with the first anniversary of 11 September says consumers have lost their trust in big business and are seeking the safety of home. It will take instinct born of experience to reach them. That's immeasurable - and invaluable.