I have a Custom Report looking at a subset of visitors over one a one week period. Specifically, the report is looking for users who match a custom dimension value.
Over a previous 7 day period, the above custom report shows 824,512 visitors. If I apply a “device type is not desktop” segment, I get 389,133. If I then apply a “device type is desktop” segment, I get 140,355.
Where did the other 295,024 people go?
To state the obvious, there are no other filter elements in the segments. The two are inverse of each other, and that’s it. All the reports are on a cron.
I switched to Matomo because the high sampling rate with Google Analytics made analysis flawed. But I’m concerned by the large gap in this case, and am hoping I’m just overlooking something silly.
Just a guess here, but sometimes “device type is not desktop” might not include visits where device type is not set. I only mention this because I ran into it on a totally separate platform. The underlying cause is when a database compares NOT LIKE, that doesn’t include NULL values, since NULL isn’t NOT LIKE, it’s nothing.
Thanks @fatica, that is a good hunch. I went to test this by applying the dimension to the Visitors>Devices page.
What I found was that when I applied the “device is equal to desktop” dimension, the Desktop number on the page did not change, but everything else went to 0 (as one would expect). However, if I applied the “device not equal to desktop” dimension, all the numbers decreased by some degree and the Desktop number went to 0. One would expect the Desktop number to go to 0, but the Smartphone number fell by 20%, which makes absolutely no sense.
This seems like a clear bug to me, unless there is some other possible explanation?