Major technology firms including Facebook, Google, Apple and Microsoft have all slowly been transitioning to a new frontier; that of a cookieless world. Where advertisers may have previously used cookies to track users clicking on ads, this type of tracking is less and less useful in a world dominated by mobile search and omnichannel consumers. Privacy concerns are also a major factor in the move away from cookies and, over the last 18 months or so, we have seen the first major steps away from cookies. Safari is making concerted efforts to lead this movement with the launch of an initiative known as Private Click Measurement or PCM.

What does PCM mean in practice?

When a user clicks on a certain ad, they are often then sent to the advertiser’s website to complete an action such as subscribe to a mailing list, download a digital asset or make a purchase. 

The user is identified while on the ad platform, before they click on an advert and are transported to the destination URL. Once that happens, and the user lands on the advertiser’s site, any additional engagement needs to be tracked so that the advertiser can measure the effectiveness of their campaigns. In absence of this data, the only trackable metric is clicks.

Previously, ad platforms have used third party cookies to identify users away from their ad platforms. This meant that any conversions could then be attributed back to the original ad click. Additionally, cookies could follow users around the web and monitor their search habits. For example, a cookie could be used to identify a user visiting a website selling used cars. We then know that search user is likely in the market for a used car, so ads for used car dealers can then be served to that user.

With third party cookies now being limited, ad platforms have moved to a different method called link decoration. This is a common practice also used by tech giants Google and Facebook (i.e. fbclid and gclid).

Safari’s solution is PCM, which is designed to measure ad clicks both on websites and from clicks in iOS apps to websites. It says, “Websites should not be able to attribute data of an ad click and a conversion to a single user as part of large scale tracking.

“At the same time, we want to support measurement of online advertising. PCM achieves this tradeoff by sending attribution reports with limited data in a dedicated Private Browsing mode without any cookies, delaying reports randomly between 24 and 48 hours to disassociate events in time, and handling data on-device.”

How does it work?


PCM was formally introduced in February 2021 as part of OS and iPadOS 14.5 betas and an on-by-default option for Safari users.

PCM limits reporting to the campaign level only. In practice this means that advertisers will be told a conversion action is attributed to the campaign ID that drove the click.

Additionally, PCM also limits the conversion actions that can be reported to 16 (as per 01 February update). These conversions won’t carry any data such as the names of the items purchased or their value.

Timeline for Change

  • May 2019: Safari proposes PCM as a privacy-preserving measure.
  • February 2021: PCM is introduced as an on-by-default feature.
  • February 2021: Safari says it is working with other web browsers to independently implement PCM so it can become a web standard.

How will PCM impact advertisers?

A glimpse into what PCM will look like can already be seen on Facebook, following the changes made to Ad Manager rolled out on January 2021. While Facebook is rolling out a different standard, Aggregated Event Measurement (AEM), in hope of making it the industry’s standard, the implications are rather similar.

For advertisers, PCM means:

·        Limited event tracking

·        Limited attribution windows

·        Delayed campaign reporting (up to 72 hours)

·        Campaign reporting will be modelled to the ad set/ad group level only

·        User attribute breakdowns (demographics, interests, etc.) will be deprecated

·        Remarketing audience sizes will reduce

·        Campaign attribution will be reduced to a seven-day click window


What can you do?

One option for advertisers to maximise their ad effectiveness with this more limited data is to optimise creatives by clicks and engagement on the ad platform itself. It’s important to note however that this won’t always correlate with actual conversions.

Key attributes, such device type, operating system and location, should also be prioritised so that you glean as much meaningful data as possible from the information you have to work with as an advertiser.

Author Rebecca

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