When we run advertising campaigns, we often find that the data provided by our ad server used to serve ads does not fully match the information collected by the web analytics tools installed on our website. The reason is simple: two different systems measure the data in different ways, in different places and not at the same time.

Our ad server - as the name implies - is responsible for serving ads and tracking clicks on them. It records exactly when someone clicks on an ad on the website. In contrast, web analytics tools measure when visitors arrive at the ad's landing page and what actions they take there, using a built-in tracking code.

This means that the ad server takes into account the "moment of click", while web analytics tools track the loading of the landing page and the behaviour of visitors. As a result, it is natural that there may be differences between the data collected by the two systems. For example, if someone clicks on an ad but for some reason the landing page does not load (for example, the visitor quickly closes the window), the ad server will register a click, but the web analytics tool will not detect the visit.

Let's look in more detail at the causes that can lead to discrepancies:

Slow website loading: if a website loads too slowly, users may close the page before the web analytics tracking codes are fully loaded. In this case, the ad server will register a click, but the web analytics tool will not record the visit.

Slow internet connection: similarly, if the user has a slow internet connection, this can also affect the loading time of the website and the tracking codes it contains. This can be particularly problematic on mobile devices, where varying network speeds can further increase the chance of discrepancies.

Different identification of the same users: if the same user clicks twice on the same ad within a certain period of time, there may be differences in how these clicks and visits are counted based on the different algorithms of the two separate systems.

Browsers and add-ons: some browsers or browser add-ons (adblockers, overly strong privacy settings) may block or limit the functionality of web analytics tracking codes. While the ad server may record the click, web analytics tools cannot track the visitor's further activity on the site.

Rejecting cookies: users are increasingly aware of online tracking and often reject cookies or limit the tracking of their web activities. This can affect the measurement of web analytics tools.

Use of cookie wall: it is common practice not to load web analytics codes on the website until the user gives his or her consent. This alone can cause many discrepancies, but in most cases users will allow tracking where the option is mandatory. The wrong solution is when the option appears at the bottom of the page while the web page remains readable. This way, users ignore the opt-in and do not select any option, so the web analytics code cannot load. If you use Cookiebot and Google Analytics, you can read about GDPR-compliant settings by clicking here.

All these factors can contribute to data mismatches between data servers and web analytics tools. The key is to be aware of this natural phenomenon and try to minimise the impact of discrepancies by improving the aforementioned solutions and website performance.