WTF is a persistent ID?

This article is a WTF explainer, in which we break down media and marketing’s most confusing terms. More from the series →

Cookies are out; persistent IDs are in.

The rise of mobile, which can’t be tracked effectively with cookies, has led to an increase in using data from logged-in users to provide more accurate and individually personalized ad targeting. Facebook was the godfather of the “people-based” marketing approach, and now many companies use it. And lately Google has started depreciating the cookie in its own products. Marketers now must use Google’s identity-based, not cookie-based, tools on YouTube for example. The notion of the persistent ID is gaining steam.

We’ve broken out some of the main points below:

WTF is a persistent ID?
This is an identifier that can provide a single view of an individual across numerous devices — across desktop, mobile web, and in-app, without duplication. This ID is formed using deterministic data (not probabilistic data), which is gathered from log-ins. If a person logs in to a social media or email account, or any online account, and remains logged-in, they can then be recognized wherever they are on the web or mobile. So for marketers, better data.

OK, and why is deterministic data better than probabilistic?
Probabilistic data provides more of an educated guess, whereas deterministic is taking direct information from details an individual has used to log-in to an online service.

Fine, so why is a persistent ID a big deal?
The cookie has always been the workhorse of digital advertising. But it doesn’t work well for mobile. “The topic of identification and how to target a consumer as they move from mobile web browser, to app and then to desktop browser is big because that online journey each of us makes on a daily basis, tells most advertisers we are three different people,” said independent ad tech consultant Paul Gubbins. “That’s not great if you are a brand trying to manage things like reach and frequency.”

Are persistent IDs also better for attribution?
Yes. And particularly figuring out mobile’s place in the mix. “Marketers will need to know about this as it will have a massive impact on how well their marketing budgets work for them,” added Gubbins.

And for publishers?
Publishers  must ensure their inventory is mapped to any type of ID the buy side has segmented their audiences against.

What about cookie IDs, and device IDs – are they the same thing? 
They both come under persistent IDs, but cookies are desktop only and device IDs device-only. Persistent is what stitches them together.

What are the pitfalls?
One of the biggest challenges is the fact that, unlike the cookie ID which is universally accepted, there is no standardization for persistent IDs. The cookie ID has been the universally accepted currency, so is still the dominant way that agencies buy inventory. The walled gardens each have their own way of tracking. And that’s different from what ad tech vendors supplying persistent IDs offer, and on from how publishers quantify it. That may create blind spots for marketers, who are used to being able to see across multiple platforms via the cookie, because walled gardens also don’t have a history of sharing information.

But in time this will be a replacement for the cookie?
In time. “We will see social and search giants reference privacy and mobile for reasons that they are migrating to their own proprietary digital IDs this year I would imagine,” Gubbins said.

Will the General Data Privacy Regulations update impact this?
Absolutely. Any service that collects some form of personal data, like email addresses, will have to comply with the new GDPR laws, and also the new ePrivacy laws. “That will 100 percent apply to deterministic IDs, like log-in information, which is personal,” said Yves Schwartzbart, IAB’s head of policy and regulatory affairs. It will be easier for companies with strong first-party data (so anyone with a scaled logged-in users) to communicate with their customer bases about what consent they need to gather data, but difficult for any intermediary companies that don’t have a direct relationship with the end customer.

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