Have you ever noticed that the number of clicks an ad-server is reporting is different to Google Analytics (GA)? And the sessions in GA don't match the number of clicks in the ad-server?
The sessions in Google Analytics are considerably lower than the clicks in the ad-server. Why is this so?
The short answer to a query like this is: you can’t compare the two. It’s apples and oranges.
For a more detailed answer, this article is very helpful: It’s from Google’s own Help section and it explains the difference between clicks and sessions and why even within Google’s own eco-system they don’t match: https://support.google.com/analytics/answer/4588315?hl=en
When someone clicks on an AdWords ad, the click is immediately recorded in the Ad-server logs. Most AdWords ad types charge the advertiser when the click occurs. There are some ad formats where the click is not always the billing event, but we'll explore non-standard cases later on.
Before a session is recorded, several things happen:
1. When the click takes place, the browser is pointed to the advertiser's landing page.
2. The advertiser's website then responds to this request and starts to transfer data from the web server to the user's browser.
5. The user's browser/device and security settings must support:
If any of the above are disabled, Analytics may not be able to record a session. Universal Analytics doesn't strictly rely on cookies and users may handle client ID in their own ways.
6. Next, the browser sends a separate request to www.google-analytics.com, the Analytics servers.
7. Finally, a session is recorded.
“The key takeaway here is that the process to record a click is straightforward; however, recording a session involves requirements and checkpoints. The whole process from click to session should happen within seconds, but if latency is introduced at any of these checkpoints, then this can in turn reduce the click-to-session ratio (more clicks than sessions are recorded).”
If you're dealing with a mobile campaign too, bear in mind that latencies are even more considerable and clicks may be generated accidentally due to ‘fat finger syndrome’. This will increase the discrepancy between clicks in the adserver and sessions in Google Analytics.
And here are a few articles dealing with the same subject (demonstrating that this is an industry-wide challenge:
Interestingly enough, a Google Search for "google analytics session ad server clicks" returns close to 3 million results.