Analytics packages (such as Google Analytics) measure different metrics than ad servers, so their reports will not reconcile with DFP.
Page views vs. impressions
Analytics tracking is based on page views. In contrast, DFP ad server concepts are, by design, not page-specific:
- An ad tag can be placed on multiple pages.
- An ad unit can be associated with many pages.
- A line item can be targeted to multiple ad units.
- A line item can serve to a single page multiple times.
Code execution
DFP counts impressions delivered to ad tags; analytics packages count the execution of analytics tracking code. Since these snippets of code are located in different parts of your page code, both scripts might not load or execute on every page view.
For instance, some analytics packages recommend placing tracking code at the bottom of your HTML. If a user exits a page before the tracking code is executed, the analytics package will not count a page view, but DFP will still count an impression.
Since there is no interaction between ad tag code and analytics tracking code, analytics packages cannot account for unfilled impressions, which can be caused by any number of variables:
- A lack of inventory
- Firewalls and misconfigured security software
- Ad blockers
- Intermittent network connections
- General latency
Iframes
Some publishers serve DFP tags in iframes. Browsers that don't support the <iframe> tag will not report an impression, but an analytics package will count a page view. Ad tags within an iframe can result in an extra round trip between the browser and server. This additional latency can cause some users to leave the page before the browser has enough time to make the calls to both the analytics package and DFP. If the analytics tracking code is present within both an iframe as well as the parent frame, the analytics software will register an inflated number of page views.
Cookies
Analytics packages typically require cookies to track page views. Some packages only record visitor traffic associated with a visitor cookie. If this cookie information is not available for a hit, or if a user has disabled cookies, then that hit may be disregarded.
Referrers
Comparing referrer URLs to DFP clicks is not advised. Referrers in analytics are not an accurate measure of clicks or landings for the following reasons:
- Referrers can be disabled by users.
- Internet security applications can block referrer data.
- Firewalls and proxy servers can filter referrers.
- Users can spoof referrers to prevent servers from knowing where they've been.
- Depending on the line creative type (rich media, standard image, etc.) and the ad tag (iframe, JavaScript, standard HTML, etc.) on the page, the referrer can be either “DoubleClick” or your domain.
- Internet Explorer does not send referrer data when switching from either (a) HTTP to HTTPS, or (b) any non-HTTP/HTTPS protocol (e.g., file://) to HTTP/HTTPS.
Source: Google Support
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