What is Google's match rate, and why does it differ from audience size on platforms like YouTube?

The match rate in Google indicates the percentage of the list that Primer sends that Google can match to an associated user they have information on. Since Primer provides a lot of personal emails, and Google has seen many of these emails before, match rates can sometimes be quite high.

However, it's important to note that the match rate only tells us how many users Google can identify, not how many users are available to be served an ad. This distinction is why you might see a significant difference between match rates and available audience sizes for platforms like YouTube.

A similar situation occurs on LinkedIn. For example, LinkedIn might report a 90% match rate, but the actual audience size can vary. In some cases, the audience size may even exceed 100% because one email address might be associated with two different LinkedIn profiles.

This discrepancy occurs because the match rate measures identification, while audience size measures the number of users who can actually be targeted with ads.