Turn on your TV during prime time and you’ll inevitably see a cavalcade of celebrity faces, ranging from Oscar winners to “Wasn’t that the guy in that show we watched that one time?” Attaching a star to your brand is something that advertisers have done since the first rock retailer made a cave drawing of Thutronk the Hunter carrying one of his store’s special stones. And yet, science says that people just don’t care, and that it may have a negative impact on your brand.

New research from the folks at ad analytics service Ace Metrix, who released a similar study in 2011, claims to confirm that celebrified ads do not generally perform as well as ads with unknown actors who hope to someday be celebrities.

In its expanded report, Ace looked at more than 1,200 ads featuring various celebrities from the worlds of TV, movies, music, and sports — they even included brand icons like that AFLAC duck in the study.

The results found that ads without celebrities continue to outscore star-studded ads in all seven facets of the Ace scoring system. It’s not a huge difference, with the overall average score for celeb ads virtually the same as regular non-celeb spots. But Ace says this underscores just how little a difference having a celebrity in your ad makes.

“Advertisers continue to invest heartily in celebrities as spokespersons or endorsers and more recently as ‘brand ambassadors’ hoping to reap financial and brand lift rewards by leveraging the popularity and social status of the public icon,” said Peter Daboll, Ace Metrix CEO. “But often advertisers ignore the risks such as the fleeting or narrow appeal of a particular celebrity. Our continuing research finds that celebrities fail to provide any meaningful impact in terms of effectiveness, as viewers often struggle with the relevance of the connection.”

That said, several celebrities fared much better than the average, with Ellen DeGeneres being one of the few celebrities that seemed to make a noticeably positive difference in consumers’ reaction to an ad.

Of course, you probably remember when the folks at One Million Moms tried to have the openly gay Ellen fired from her gig shilling for JCPenney. Guess those million moms weren’t part of the Ace study.

Next on the list, with slightly more than half the measured positive impact of Ellen, was Dean Winters, known to 30 Rock fans as Dennis “Beeper King/Subway Hero” Duffy but more popularly recognized as “Mayhem” from the series of Allstate insurance ads.

Other celebs with some value to an ad include handsome actor Paul Rudd, Super Bowl champ Ray Lewis, Green Bay Packer Greg Jennings, and actress/America’s girlfriend Emma Stone.

Interestingly enough, the bottom of the celeb ladder is occupied by a name that sells massive amounts of music, apparel, concert tickets and all manner of other items — Jay-Z. In spite of his huge and varied empire, the rapper and businessman had the lowest score of the celebs featured in ads. So people love his products but apparently just don’t want to see him mope his way through a TV ad.

In terms of individual ads that worked, the top-scorers on Ace’s study are not big-time box-office stars, but athletes, musicians and TV stars. In fact, three of the top-10 ads feature gymnast Jordyn Wieber. Other sports figures in this list are NBA star Dwyane Wade and yet another Green Bay Packer Aaron Rodgers.

Wade can now trash-talk his Miami Heat teammate LeBron James, whose Samsung ad was among the 10 lowest-scoring celeb ads in the Ace study. He was joined by fellow athletes Justin Verlander of the Detroit Tigers, and Oakland Raider (and former Packer) Charles Woodson.

And while we’re on the topic of half-hearted celebrity endorsements:

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