Segments are applied before sampling in reports.
Analytics applies segments after it samples the property-level data, and after it applies filters, which can also reduce the number of sessions included in a sample.
In data analysis, sampling is the practice of analysing a subset of all data in order to uncover the meaningful information in the larger data set. For example, if you wanted to estimate the number of trees in a 100-acre area where the distribution of trees was fairly uniform, you could count the number of trees in 1 acre and multiply by 100, or count the trees in a half acre and multiply by 200 to get an accurate representation of the entire 100 acres.
This article explains the circumstances under which Analytics applies session sampling to your data in order to give you accurate reports in a timely fashion.
Default reports are not subject to sampling.
Ad-hoc queries of your data are subject to the following general thresholds for sampling:
- Analytics Standard: 500k sessions at the property level for the date range you are using
- Analytics 360: 100M sessions at the view level for the date range you are using360 thresholds vary according to how queries are configured. For detailed information, contact your 360 support team.
When sampling is applied
The following sections explain where you can expect session sampling in Analytics reports.
Analytics has a set of preconfigured, default reports listed in the left pane under Audience, Acquisition, Behavior, and Conversions.
Analytics stores one complete, unfiltered set of data for each property in each account. For each reporting view in a property, Analytics also creates tables of aggregated dimensions and metrics from the complete, unfiltered data. When you run a default report, Analytics queries the tables of aggregated data to quickly deliver unsampled results.