Sampling in Analytics is the practice of selecting a subset of data from your traffic and reporting on the trends available in that sample set. Sampling is widely used in statistical analysis because analyzing a subset of data gives similar results to analyzing all of the data. In addition, sampling speeds up processing for reports when the volume of data is so large as to slow down report queries.
As a Visiolink client with a high number of users, you might be subject to sampling. You can always see when Google is using a sample instead of all the data. This is shown as a small message just below the date range picker:
When the number is lower than (100% of sessions), Google is sampling the data. The sampling will therefore produce different totals depending on the level of sampling. The data will often still be accurate but it will not be exactly the same numbers. Two reports might produce slightly different totals at different sampling levels. When comparing the same query on the different days, the result might therefore be slightly different. Be aware that sampling does not happen unless you have a large amount of data. It is difficult to locate the exact threshold but large clients tend to experience sampling. Our recommendation is to be aware of sampling and keep it in mind when creating queries for large amount of data.
There are a few ways to avoid sampling:
- Reduce the data range
Ask yourself if the large data range is necessary to achieve what you are trying to achieve. Often smaller amounts of data will suffice when looking for a pattern or information within the data.
- Query partitioning
If you want to look at data for a longer period, you can split the queries into smaller pieces. For example if you want to look at one year’s worth of data, query data for one month at a time and export it.
- Invest in Google Analytics Premium
You will not be subject to sampling when using Google Analytics Premium. However, it comes with a high price.
You can more about sampling on Google’s website: https://support.google.com/analytics/answer/2637192?hl=en
Feel free to contact us with any questions you might have regarding tracking and Google Analytics.