The news: Weeks before Upfronts, Nielsen received some bad news. The Media Rating Council (MRC), an independent body that certifies TV measurement products, posted a statement saying it had found “unusual changes in measurement results” with Nielsen’s Big Data + Panel product dating back to at least early 2025 based on “various sources” and its audit work.

Among the issues MRC found were:

• A 10% decline in total day impressions for consumers ages 25 to 55 during H1 2025 as compared with H1 2024.
• “Issues with representation levels in Nielsen’s panel,” including demographic and household viewing data.
• Changes in the variability between Nielsen’s Big Data + Panel and standalone Panel-only results.

The MRC clarified that it’s still certifying Big Data + Panel and that Nielsen has already made progress toward addressing the problems.

Zooming out: The MRC statement could undermine confidence in Nielsen’s Big Data + Panel measurement, putting it in an awkward position with little runway until Upfronts, the highest-profile TV ad buying period of the year.

• Long the industry leader for TV measurement, Nielsen has had a rough transition into the 2020s and now faces a field flush with competitors that have backing from major broadcasters.
• Its most notable competition includes iSpot, Comscore, and VideoAmp—each with a mix of support from NBCUniversal, Disney, Paramount, Warner Bros. Discovery, and others.
• Those competitors, which gained ground offering digital and cross-platform measurement as Nielsen was still getting Big Data + Panel off the ground, have been adopted by more marketers each Upfront season, though Nielsen is still the most-used measurement provider.

This isn’t Nielsen’s first run-in with the MRC. In 2021 the MRC withdrew its (now-reinstated) accreditation for Nielsen following miscounting during the pandemic. Additionally, the NFL accused Nielsen just days before the start of the 2025 season of undercounting “millions” of football viewers.

Implications for marketers: Nielsen’s MRC snafu comes at an unfortunate time for the legacy measurement leader and is a serious blow to confidence in its effort to combine its historic panel-based data with digital viewing signals.

If ad budgets shift further toward Nielsen’s competitors this Upfront season, it could be a reflection of that shaken faith. However, its yearslong position as the industry leader could help soften the blow.