Unfortunately, data discrepancies cannot be fully avoided. The normal range for that is considered 15%, but there may be variations depending on the following:
1. Latency: slow server response or internet connection on the user's end. When a response is taking too much time we might lose data and not count the impressions. This may also happen when user’s internet connection is slow and a page is closed before an ad is served.
2. The more steps in redirection, the more discrepancies are possible, due to the longer response time.
3. Differences between our platform and how advertisers count:
a. Advertisers may count only unique events, while we count every request.
b. Overcapped impressions are not attributed to general statistics, while clients may count them.
c. Impressions attributed to Fallback for some reason, which may be due to incorrect targeting.
4. Usage of Adblock (or any other ad blocking software).
5. Pack. Mobile pack tends to be slower and a user can close the page before ad has loaded.
6. Tracking set up by the advertisers themselves. Note, that an incorrect traffic setup can result in up to 100% of a discrepancy. (Usage of 3rd party tracker may also increase discrepancy.)
7. If a client uses a prepopped zone, he will always count more impressions, where we might not get all the data.
The discrepancy cannot be covered only by points stated above, but combinations of these might affect it heavily.