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The instructions in this help article may be affected by recent changes in the Analytics user interface. See this blog post for details. Help center updates are coming soon.

About sampled data

Understand what sampling is, and why it's happening.

Sampling in Google Analytics (or in any analytics software) refers to the practice of selecting a subset of data from your traffic and reporting on the trends detected in that sample set. Sampling is widely used in statistical analysis because analyzing a subset of data gives similar results to an analysis of a complete data set, while returning these results to you more quickly due to reduced processing time.

In Analytics, sampling can occur in your reports, during your data collection, or in both places.

In this article:

Sampling in reports

When a report is based on data from a large number of sessions, you may see the following notice at the top of the report: This report is based on N sessions. This notice alerts you that the report is based on sampled data. Sampling occurs automatically when more than 500k sessions (100M for Analytics 360) are collected for a report, allowing Analytics to generate reports more quickly for those large data sets. When your report is based on sampled data, you have the option to adjust the sample size to increase accuracy or increase speed. Note that Flow Visualization reports are sampled after 100,000 sessions and 1 million conversions in the Multi-Channel Funnel reports.

Analytics 360 account users can also create unsampled reports.

Within 48 hours of being upgraded to Analytics 360, views receive a 13 month backfill of precompute data. Precompute supports lower-latency queries on historical data up to, but not exceeding, 13 months before today's date (on a rolling basis), and increases the sampling size from 500K to 100M sessions. Precompute process up to 1000 sessions per user.

Sampling in data collection

If you have many millions of sessions per month, you should consider configuring your tracking code to sample your traffic, or collect data from a subset of your total traffic. Sampling your traffic allows for accurate reporting without a decrease in processing speed.

Learn how to set up collection sampling for different tracking methods using the appropriate Developer Guide for your environment:

Learn more about sampling and how sampling works in Analytics.

Related resources

How sampling works in Analytics






Refer to the sampling configuration option in the Analytics (Universal Analytics) tag if you use Google Tag Manager to manage your Analytics tracking.


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