Marketers have done so much to blur the line between entertainment and advertising that it’s often hard for consumers to tell the difference. But here’s an interesting little factoid from a new Association of National Advertisers survey of 73 client-side marketers. The folks who decide whether to use product placements and other tactics to mess with our minds don’t really know whether they work. Branded entertainment is supposed to give audiences warm feelings about a company or product, but nearly two-thirds of the surveyed marketers say that they’re unhappy with the quality of the research about its effectiveness. That’s the second-biggest concern, after cost, cited by those who don’t use branded entertainment. ANA chief Bob Liodice says it is “up to the internal researchers, media providers and agencies to better measure branded entertainment integrations.” The lack of persuasive research may explain why the number of marketers using TV for branded entertainment has fallen 10% since 2006, the last time the ANA conducted the survey. (We don’t know how many of the marketers still put branded entertainment on TV; the ANA just disclosed selected facts in a press release — not the complete data.) But the number of client-side marketers using Internet films to promote their brands has more than doubled to 31% over the same five-year period, while 55% use the Web for other forms of branded entertainment, up from 28%. Promotional entertainment is up 20% at sports venues.