The research, conducted in partnership with an undisclosed national retailer, sought to accurately measure the impact of Internet display advertising across online and offline sales, by tracking people who had registered with both Yahoo and the store. The research found an approximately 5 percent increase in spending among those who had seen the ads–with 93 percent of those sales occurring in stores.

The potentially worrisome thing, however, was that among those under 40, the percentage was nearly zero. That could reflect the unpopularity of the particular retailer among that demographic. Or it could underscore a growing immunity to display advertising among the Web-savvy younger generation.