• by Laurie Sullivan  @lauriesullivan, November 9, 2011

Search on mobile devices continues to fuel marketing campaigns, but attribution management tools must evolve to take full advantage of the 16% to 22% mobile marketing ad spend that Efficient Frontier estimates will materialize by 2012.

The majority of searches that begin on a mobile device end on desktops or in stores.

eMarketer estimates that U.S. marketers will invest almost $4.4 billion in mobile advertising by 2015, up from $1 billion this year. Local retailers continue to lead the trend, along with more sophisticated mobile devices. Smartphones and location-based services continue to drive mobile search traffic to physical stores, per the research firm.

Tracking attribution across channels -- desktop, mobile, television and other connected devices -- will become a key strategy. While return on investment for mobile search continues to climb, it still remains less than half of desktop search, said David Karnstedt, Efficient Frontier president and CEO.

The findings from the study -- released Wednesday with equity research firm Macquarie Securities -- reveal that mobile marketing investments rose to 6.5% this year, up from 2.7% in the previous year. The study combines about 3 billion monthly impressions from approximately 30 Efficient Frontier customers.

The ROI for mobile campaigns rose five times in the past six months, according to Siddharth Shah, senior director of business analytics at Efficient Frontier. When the company reported mobile search numbers in February, the ROI stood at about 10% of desktop. As better devices emerge, the return continues to rise, he said.

"Anecdotally, I know several large national brands are seeing about 15% to 20% of the impression volume coming from mobile campaigns," Shah said, but it's important to consider the investment returns on branded and non-branded keywords and compare how each converts on a desktop.

The differences between mobile and desktop search metrics are becoming more clearly defined. Mobile phone search campaigns have a 66% higher click-through rate compared with desktop, and 37% higher than tablets. The cost per click (CPC) for mobile phones is 8% higher compared with desktop, with tablet CPCs accounting for 85% of their desktop counterparts.

Marketers have been increasing investments in tablet search campaigns, too. Tablets have contributed 43% to Efficient Frontier's mobile search spend and 50% of click share since August. Retail clients appear to lead the way, with 77% of mobile search spend attributable to tablets.

User behavior and search-query length differs when comparing desktops to mobile phones to tablets. Apparently, mobile devices continue to lengthen the total time that people spend online. Desktop queries are the longest, with about 2.6 words, followed by tablets and mobile phones. While the screen size matters, expect to see more complex mobile queries as voice search become more popular and easier to use.