Generally speaking, data from web analytics programs such as Google Analytics will differ than first-party ad servers. We generally don't see a large variance, but most often when there are discrepancies it is because of a variety of factors, including comparing clicks to visits. Here are a few examples:
1. Visitor browser preferences:
2. Tracking methods:
There are two main methods of tracking activity: cookie-based and IP + User Agent.
Google Analytics is a cookie-based analytics program. As such, it relies on a browser setting the cookie. If cookies are disabled, this type of program will not count the visit.
Polyvore uses IP + User Agent tracking. This tracking method uses log file analysis. This may report higher numbers than reported by cookie-based tracking because of dynamically assigned IP addresses.
3. Reporting Limits:
Google Analytics limits a site visit per user to one time every 30 minutes (by default). Ad servers, by comparison, do not filter such behavior, but recognize the fact that it is a unique visitor (using a cookie) coming to the page more than once. So impressions will be counted separately from unique impressions. Google simply filters the multiple impressions and provides the unique impression.
4. Comparing Apples to Oranges – Clicks vs. Visits:
There is an important distinction between clicks recorded by Polyvore and the visits recorded by Google Analytics. The clicks column in a campaign report refers to how many time the advertisement was clicked by visitors while visits in a Google report indicates the number of unique sessions initiated by visitors.
A visitor may click an ad multiple times. When one person clicks on one advertisement multiple times in the same session, the ad server will record multiple clicks while Google Analytics recognizes the separate page views as one visit.
5. Partial Page Load:
A visitor may click on an advertisement, but prevent the page from fully loading by navigating to another page or by pressing their browser's Stop button. In this case, Google Analytics’ tracking code is unable to execute and send tracking data to the Google servers. However, the ad servers will still register a click.
6. Other Reasons Causing Discrepancies between GA and Polyvore tracking:
Third-party images: Some browsers give users the option to disable images that are requested from domains other than the current page. Disabling such images will prevent data from being sent to Google Analytics.
- Filters/settings: Many web analytics solutions provide data filters. Differences in the way that filters are applied, or creating different filtering altogether, can drastically affect the data in your reports.
- Time zone differences: If your web analytics solutions group data using different time zones, your daily or hourly data will be affected.
- Caching: Google Analytics directly calls Google's servers each time a page is visited, even if the page has been cached. Other analytics solutions may not record an additional visit if the page is pulled from a user's or server's cache.
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