decrease observed for adgroup impression stats (over 15 min. interval)

[Evan]

Our API integration involves displaying the change in impressions over time. We pull an AD_PERFORMANCE_REPORT for each active adgroup at 15 min. intervals, calculate the difference over time (by simple subtraction), and finally graph the results. We store the absolute counts at each time of refresh (not the relative difference). 

For multiple ad groups, there have been instances where the impressions count will actually decrease compared to its previous values. This decrease is observable in the stored Performance report (absolute) values and does not appear related to our change over time calculations. While this is an infrequent occurrence, it seems quite illogical, and I'm wondering a) whether this is a noted behavior for the reporting API, b) whether our stat-refresh interval must be extended to ensure accuracy. Indeed, the minimum granularity for impressions over time using the Adwords GUI is "daily"...

Thanks!

[Sreelakshmi Sasidharan (AdWords API Team)]

Hi Evan,

The performance data is not available instantly and there could be data discrepancy if the data is pulled before stats are calculated. It is recommended to rerun the reports later to pick up any adjustments if the reports are being run for the current day or the previous day. 

Please check our documentation on Data freshness for better clarity.

Thanks,

Sreelakshmi, AdWords API Team