Carat on Wednesday said it forecast 6.4 percent growth in global ad spending in 2008, and did not revise its forecast of 5.8 percent for 2007, only slightly less than the 5.9 percent growth in 2006, writes MarketingCharts. Carat is Europe's biggest media-buying firm and a unit of Britain's Aegis.

In 2008, the Beijing Olympics will drive further acceleration in growth rates in the US and Asia-Pacific to 5.6 percent and 9.3 percent, respectively, with the US market receiving a boost from the presidential election, Carat said.

Online - the single biggest driver of ad spend growth in every region and country - "will continue to outgrow the rest of the industry by some margin, but we would also expect to see increasing impacts from new hardware and technologies, including 3G, HD radio and multi-casting and IPTV and other forms of interactive broadcasting," according to Carat.

Globally, after digital, the next two fastest-growing media are out-of-home and cinema.

In publishing, newspapers are usually the slowest growing segment, with free titles generally taking advertising share and magazines outperforming newspapers in the majority of markets, according to the forecast.

A regional ad spend breakdown and more details of the US forecast are available at MarketingCharts.