March 23 (Reuters) - Nielsen Holdings Plc is expanding its measurement of digital ad campaigns on mobile devices across the world and is adding seven new countries and Puerto Rico, the company is expected to announce on Wednesday.

The U.S.-based advertising tracking company aims to have digital campaign measurement in 25 markets by the end of 2016, representing more than 80 percent of global digital advertising spending, Steve Hasker, chief operating officer at Nielsen, told Reuters in an interview on Tuesday.

“For a brand manager interested in a global read of their campaigns, this data is exactly comparable to what we do in television,” Hasker said, referring to Nielsen’s television ratings, for which it is known in the United States.

Nielsen is launching its digital ad ratings in Poland, Turkey, Hong Kong, Taiwan, South Africa, Puerto Rico, Ireland and New Zealand.

Consumer goods companies looking to expand their reach have shown interest in metrics for South Africa, Poland and Turkey, in particular, Hasker said.

Nielsen’s global push of its digital ad ratings comes two months after its main competitor in the measurement of digital campaigns, Comscore Inc acquired Rentrak Corp, which uses set top box data to track TV viewership.

Many in the industry have wondered if the newly merged entity will be a threat to Nielsen, the dominant force in the industry.

Until now, Comscore’s ability to measure digital campaigns internationally has been an advantage, said Brian Wieser, a Pivotal Research analyst.

“This is helpful for Nielsen in that sense,” he said.