Nielsen ratings + sub second telemetry on subscription streaming data.
They still exist after having adapted to digital streaming and subscription platforms. Now they have second grain details of what is being watched which they sell to digital platforms as a data service.
The subscription platforms have even finer grain details and can use the Nielsen data to correlate switching streams to the point in time of ads. So they can model whether people watch the ads.
Source: Telemetry Data Engineer.
Latest Answers