@StanGromer Apologies if the response resulted in more of a confusion. Let me try to provide some more details in an attempt to clarify.
The first two causes I mention,
1. The data should not retroactively change unless we(The community analytics team) have re-processed and backfilled data for a historical time period for a specific reason.
2. the data processing sees some issues which could induce delays. These are rare occurrences and none of it occurred in the time period that's referred to here 23rd May - 29th May. If delays/changes in data occur, we post notifications on the Community Analytics Status Page
3. You start by saying the data should not retroactively change, yet finish with the fact it could be off randomly by 1%-2% at any time.
This might be a misleading statement.
The approximation algorithm won't result in random variations, it will take effect only if :
The data is being queried cumulatively across days and months and
There are overlapping visits (explained below) across those time periods.
Also this is only for Unique Visits and Unique Visitors.
Reference to the algorithm on the backend. https://www.elastic.co/blog/count-elasticsearch
However for a fixed time period being queried, data should remain same each time.
Some more details on the scenarios for overlapping visits.
1. Overlapping visits across 2 months
'Visits' is defined as the number of unique user sessions. A session is defined as a group of interactions one user takes within a given time frame. Session times out in the case of 30-minute inactivity.
Assume that a user was browsing through a community during the last hour of a month (Month-1) and he/she continued browsing through the first hour of next month (Month-2)
When we measure visits for Month 1, this user's session will get counted as 1 visit
When we measure visits for Month 2, this user's session will get counted as 1 visit
So, if you sum up visits for Month1 and Month 2, you will get 2.
Whereas, if you measure visits for the entire 2 months time period, this user session will be counted as a single visit.
Hope this explains.
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