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Approx Count Distinct vs Unique Vsitor


Community Advisor

Hello everyone,


I am comparing Approx count Distinct Visitor that is calculate on Customer ID with Unique Visitor. When I compare these two values I expect a Unique Visitor > Approx count Distinct but in some cases, it is smaller. Any suggestion?




2 Replies



Dear Luca,

What if the same Laptop is used for multiple logins? One Unique Visitor and multiple Customer IDs. Not possible?

Thanks, Arun.


Employee Advisor

Hi @Luca_Lattarini ,

Are the number of customer ID crossing the uniques exceeded limit? In that case, it will be counted as 1 item. Also, please note that the function uses the HyperLogLog (HLL) method of approximating distinct counts.  It is configured to guarantee the value is within 5% of the actual value 95% of the time. So, it's not 100% accurate always.