When cookies are disabled by a visitor (cookie-less tracking), how does it impact Matomo reports accuracy?
There are various cases where cookies can be disabled: when the browser has cookies disabled, or when the Matomo JavaScript code runs cookie-less (disabled cookies via call to disableCookies()), or if you are importing server logs in Matomo which do not contain cookie information.
When cookies are disabled, some data in Matomo will be less accurate.
You’ll find below the complete list of metric and reports affected. All other reports which are not mentioned below will still work the same.
Unique Visitors and New VS Returning visitors metrics will be inaccurate
Matomo uses cookies to store a unique visitor ID, used to recognize visitors from previous visits. When cookies are disabled, Matomo will still be able to determine unique visitors based on IP address and other footprints, but this will be inaccurate. So the following metrics will be inaccurate: Unique visitors, New visitors, Returning visitors.
Goals and Ecommerce conversions will be attributed to the channel used in the visit that converts
Ecommerce and Goal tracking attribution is also affected. By default, Matomo stores the website or keyword or campaign used to find your website in a cookie, so that we can credit (attribute) this website when the visitor makes a conversion (Goal conversion or Ecommerce order). When the conversion happens in the same visit, Matomo will be able to credit the website referrer (even if cookies are disabled).
However imagine the following use case: the visitor uses a newsletter link tagged with a campaign parameter, then visits 5 pages on your website but does not buy. She then comes back 2 hours later directly typing your website URL (therefore a Direct Entry visit), then buys during this second visit. When cookies are enabled, Matomo credits the conversion to the initial Campaign. When cookies are disabled, the conversion is not attributed to the original newsletter link as this data is not available.
Multi Attribution and Cohort reports won’t show data
Because all conversions will be attributed to the channel used in the visit that converts, Multi Attribution reports for multiple channels and Cohorts reports won’t be able to show data.
A small limited number of other reports will be inaccurate
The following reports won’t display accurate data anymore, because all visits without cookie will be counted as if they were new visitors, making the report inaccurate:
- Days since last visit
- Visits by visit count
- Visits to Conversion
- Days to Conversion
See also: How does Matomo detect unique and returning visitors?