1. Why are there differences in measurement when using a Site Analytic software compared with when using an Ad Server in measuring impressions?
This article provides a good explanation https://support.google.com/dfp_premium/answer/177507?hl=en.
2. Why are the numbers between XPO reporting different or not matching with the numbers from other reports /systems? Why is there such discrepancy?
There are multiple reasons for this. Such discrepancies could be due to XPO and your other tracking partner are measuring different things e.g. when XPO delivers click number, we apply our own proprietary methods of de-duplication and fraud screening. We follow all industry best practices in the design, operation, and both internal and external monitoring of the click redirect handlers. This discrepancy would also occur between systems e.g. Google DFP vs Google DCM and Google Analytics vs DFP. Also, the placements of the trackers would also make a difference.
3. Why is there a discrepancy between Google Analytics and XPO?
Google Analytics (GA) is a tool meant for measuring website traffic. It is not meant for counting ads impressions. In the case of measuring "clicks" and "visitors", GA counts “visitors” whereas XPO counts “clicks”. Google counts “visits” using a proprietary algorithm with a 30-minute sliding window. The GA numbers are de-duplicated by IP address over a 30-minute sliding window (repeat clicks in the window are counted once). XPO clicks are counted as they occur, with a 1-second de-duplication window.
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