GA is failing a simple addition! N. of unique visitors wrong
I run a site that this month so far has well exceeded 1,000 unique visitors per day and even 2,000 in a few cases, except for one day when the toll stopped at 900-ish.
But if I go in Audience Overview and filter the time selection from 1 to 21 February, the returned total of unique visitors is 22,085, which immediately seemed strange. So I noted down and added the numbers of unique visitors per single days from the same panel in Audience Overview, and what I get is over 29,000. How can GA be failing a simple addition?
The count doesn't add up even if I run a check on just any two days. For instance, on the 10th I had 2,013 unique visitors, on the 11th they were 1,771 – that's 3,784 in two days. But if I select the 10th and 11th with the calendar picker, I get 3,584. That's 200 lower. And I'm just realizing that this has always been the case. Even if I do tests for months back, the calculations are always wrong.
Does anyone have any clue about this?
Re: GA is failing a simple addition! N. of unique visitors wrong
While it may appear that way, GA is not failing at math. What you need to keep in mind is that as you change your date range; GA changes the calculation of unique users. Let's take your data to illustrate:
"For instance, on the 10th I had 2,013 unique visitors, on the 11th they were 1,771 – that's 3,784 in two days. But if I select the 10th and 11th with the calendar picker, I get 3,584"
Feb 10: 2,013
Feb 11: 1,771
Feb 10&11: 3584
What that means is that on the two days (Feb. 10 & 11), there were 200 users that came on both days. So in other words; using the date range picker does not give you a rolling total of uniques but an actual count of the total unique visitors in the date range.
Although it's not as plainly written more on that here: