NEW YORK: Television advertising featuring celebrities tends to fall short when it comes to making a positive impression with viewers, new figures show.

Research firm Ace Metrix tested 263 such spots that were broadcast nationally last year, covering 110 brands from 16 sectors.

It defined the overall impact in terms of persuasiveness and watchability, asking between 498 and 608 people to state whether ads seemed relevant, informative, likeable, held their attention and changed perceptions.

"Of the 263 celebrity ads tested, only 31 exceeded [a] 10% lift. In other words, only 31 celebrity ads did better than 10% above their respective industry average," the company's study argued.

More specifically, commercials starring household names - representing approximately 15% of all TV spots - under-performed those that did not across every metric assessed.

"An ad featuring a celebrity - on average - was rated nine points lower than ad without a celebrity," the report argued.

"To be clear - on average - having a celebrity in an ad detracted from the ad's effectiveness compared to the industry average by 1% among the demographic target the ad most appealed to."

The gap stood at just seven index points concerning watchability, as creative based around a famous leading man or lady generated 571 points, measured against 578 points where this was not the case.

Totals hit 544 points and 570 points for boosting products' desirability, and 550 points and 574 points for relevance.

Difference levels also reached double-digits while monitoring persuasion, engagement, likeability and information, and nine points regarding altering consumer perceptions.

"Fewer than 12% of ads using celebrities exceeded a 10% lift, and one-fifth of celebrity ads had a negative impact on advertising effectiveness," Peter Daboll, ceo of Ace Metrix, said.

Oprah Winfrey secured the best returns, delivering three of the four most effective commercials, promoting Liberty Mutual Auto Insurance and Progressive Insurance.

These efforts yielded an average uptick of 27%, indicating Winfrey's cachet with a broad audience.

Well-known faces from some of the 52 ads witnessing negative results included Tiger Woods, Lance Armstrong, Jamie Lee Curtis, Andie MacDowell and Joe Montana, all described as "multiple offenders."

Data sourced from Ace Metrix; additional content by Warc staff