Netflix rarely releases viewership numbers, arguing that, because it doesn’t court advertisers, it can safely sit on its own data. That mindset is changing, however, as competition heats up in free ad-supported streaming TV services. Tubi and Viacom’s Pluto TV have released viewership numbers — 20 million for the former and 15 million for the latter — but they don’t use independent measurement firms such as Nielsen or Comscore. Advertisers continue to be wary without such third-party verification.

The Wall Street Journal reports that Dunkin’ Brands Group vice president of media Keith Lusby calls third-party verification “table stakes.” He said that advertisers are spending dollars on such streaming platforms “but you’re not going to go too far until you have verification services.”

Streamers have even more incentive to use third-party verification; according to SwellShark chief executive Nicholas Pappas, “advertisers spend two to four times more money on services with data from a Nielsen or a Comscore than they spend on services without it.”

Further, a Magna Global forecast reported that U.S. ad revenue for streaming services are set to increase 39 percent to $3.8 billion in 2019, even as “the national and local traditional TV market will decline 8 percent this year.”

Streaming service Xumo just adopted Nielsen’s Digital Content Ratings, “which measures the audiences viewing shows and movies,” and sources said that Nielsen is also in talks with Roku, Pluto TV and Tubi. “We feel it’s important to bring transparency and third-party measurement to our industry to benefit all stakeholders,” said a Pluto TV spokeswoman. “We’re taking a leadership position by having early conversations with key industry players to develop ideas and identify solutions.”

But signing on to independent rating services doesn’t provide advertisers with all the data they desire. Roku, which uses Nielsen’s Digital Ad Ratings, only states that “it’s one of the top five apps on its platform by reach” — and won’t describe how it defines reach.

The service, which sells targeted ads across its platform, “doesn’t break out ad performance for its Roku Channel.” Instead, the platform, which hosts “myriad streaming apps,” only releases “data in the aggregate.” For example, it stated that “its overall platform averaged 29.1 million monthly active users in the first quarter.” A sports campaign running on Roku could appear on apps from Fox Sports, ESPN, Bleacher Report and NBC Sports, but the advertisers would only know the number of impressions.

One media buyer stated that marketers would like to know “more precisely where consumers encountered their ads.” Another buyer added, “it always pushes the conversation toward ‘How much of my inventory was delivered in premium apps versus the long tail?’” MoffettNathanson analyst Michael Nathanson concluded, “the industry eventually will require a third-party arbiter.” “There needs to be some kind of standard,” he said.