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Historical Count = 1st: Uniques & Totals are Different

  • 18 November 2022
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In Segmentation, if I pick any event and set “Historical Count”:”1st” there’s a noticeable difference between unique users and total events. Any ideas why? It seems that if a user can only be counted once anyway (because it's the user's first time firing the event), that the unique and total might be the same. Any ideas? Thanks. 

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Best answer by Matrak 21 November 2022, 15:16

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Hello Anthony, 

- The TOTALS formula calculates the total number of times an event was triggered.
- The UNIQUES formula calcultates how many unique users triggered the event.
Using “historical count = 1st”, we could expect no differences between the two.

My guesses are the following: a unique user could be using several devices to trigger the event before being identified as a single unique user by Amplitude (by logging in on the several devices they used for example). This difference could be either the sum of these “historical count = 1st” on different devices, a user launching the event several times quasi-simultaneously, or any other chronological issue happening somewhere in the tracking and definition of the “historical count” property. 

You can also visit the Amplitude help page describing how “Historical count” is calculated, which states that Amplitude's definition of "Nth time" is itself time-limited’. This could be another pist to explore.

These are my guesses and I am unsure that they are correct. I encounter a similar difference using my population. Hope I could be of some help. 😄

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