Segments are applied before sampling in reports.
True
False
Explanation:
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.
https://support.google.com/analytics/answer/2637192?hl=en
About data sampling
In data analysis, sampling is the practice of analyzing a subset of all the data in order to uncover the meaningful information in the larger data set. For example, during an election cycle, you hear lots of news about what percent of voters prefer one candidate over another, or are for or against a certain issue. Because there can be tens to hundreds of millions of voters in an election, and because the companies conducting the surveys want to get their information out to the public as soon as possible, trying to question every voter for every new survey would be extraordinarily expensive and take too much time. To solve those problems, surveyors use what they conclude is a representative sample of the overall voter population, often just 1000 voters from the millions who are eligible.
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.
In general, session sampling works well for Top-N queries and other queries that have a relatively broad, uniform distribution across sessions.
Session sampling can be less accurate for “needle in a haystack” problems like single-keyword analysis and long-tail analysis where the data is more sparse.
It is also less accurate for heavily filtered views or for conversion analysis where conversions constitute a small fraction of sessions. In these kinds of situations, refer to Unsampled reports for one-time reporting and to Custom Tables for ongoing unsampled reports on a specific data set, both available to Google Analytics 360 accounts.
Sampling thresholds
While sampling thresholds vary between Standard and 360 accounts, and among report types and query types, these are the general thresholds:
Analytics Standard: 500k sessions for the date range you are using
Analytics 360: 1M – 100M sessions for the date range you are using
360 thresholds vary according to how data is processed, how queries are configured, and ongoing development in Analytics. For detailed information, contact your 360 support team.
When and how sampling is applied
The following sections explain the circumstances under which sampling is applied.
Filters and segments
Analytics samples session data at the property level, and then it applies view filters to include or exclude sessions that meet the filter criteria. As such, data for a filtered view can have fewer sessions included in the sample.
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.
Analytics 360 samples session data at the view level, after it has already applied filters, so filters don’t impact sampling in this case. However, Analytics 360 does apply segments after sampling, so there may be fewer sessions included when you apply segments to a report.
Standard reports
Standard reports are listed in the left pane of the Analytics interface.
Analytics stores one complete, unfiltered set of data for each property in each account.
For each reporting view in a property, Analytics creates a set of tables that include data that is aggregated from the complete, unfiltered data set. When you run a standard report, Analytics queries these tables of aggregated data to quickly deliver unsampled results, for example, the number of sessions initiated by each age group during the time frame you chose.
No sampling is applied to standard reports unless you alter the data and thereby generate a new query, for example, by applying a segment or secondary dimension.