They said the way forward lay in the industry joining forces to set standards.
Peter Hirschfeld, Audi China senior manager for marketing and public relations, and Victoria Henderson, Universal McCann Asia-Pacific worldwide account director, said research and measurement was one of the biggest issues that outdoor needed to address.
Said Henderson: "It is absolutely necessary for the industry to get together to start setting benchmarks."
Hirschfeld added that proactivity and consolidation were some solutions to the problem.
He revealed that Audi only recently began using the outdoor medium in China, with spend accounting for five per cent of the automaker's total marketing budget. But Hirschfeld stressed that he would be hard pressed to increase the spend if there was a lack of accountability.
But Eric Newnham, the worldwide chief executive officer of Poster Publicity Group, believed that any solution to the issue would be ambitious because the markets in Asia were still in the developmental stage, underlined by the fact that the industry was fragmented.
"If the industry can come together, it is a sign of a mature market," Newnham said.
Sam Lam, vice-president of media services of Tom Outdoor Media Group, illustrated the point by saying that in China, the top three companies could lay claim to just 10 per cent of the total market.
Steven Yung, chairman of Clear Media, believed that consolidation was imminent.
He stressed the point by saying that with more than 80,000 operators in China alone, consolidation would be absolutely necessary.
Yung added that outdoor would continue to grow strongly in the foreseeable future. "Outdoor advertising fits in perfectly with the urbanisation of China, he said.
Lam agreed but stressed that the industry faces major challenges, especially in China.
"The industry will grow with entry to WTO and the market will expand further. But the industry is still small because customers in China, especially local ones, don't see the benefits of outdoor advertising. They also don't know who to contact because it's too fragmented, he said
Meanwhile, John Dollisson, general manager of business development of Eye Corp, Australasia, gave tips on how to produce impactful outdoor advertising campaigns.
"Size is still king and the most effective form of communication, he said.
In his research, he also found that artwork was more effective than photography, black and white posters were more easily recalled and the less colour, the better.
Other key factors included the campaign period - a one-week burst was just as good as a campaign running two or more weeks - location and the use of humour and intrigue.
Dollisson added that the impact was higher if the product had an easy name to remember.
The conference was the third of its kind to be organised by media. The event was sponsored by Poster Publicity and the Lightship Group.
