Sampling is applied to reports before segmentation.

In data analysis, sampling is the practice of analyzing a subset of all data in order to uncover the meaningful information in the larger data set. Analytics Standard and Analytics 360 both apply segments after applying report filters and after sampling, which means that a segment may include fewer sessions than are included in the overall sample. Analytics periodically adds new reports, and sometimes makes changes to the way metrics are calculated. If the date range of a report includes a time before the report was added or before a metric calculation changed, then Analytics can issue an ad-hoc query and the data might be sampled.