How do Looker calculate average session duration?

[buenolcs]

I'd like to understand how this math is done. When I take those data and calculate the average in Excel or PowerBi, the average time duration is: 00:06:18, but in Looker is 00:04:39. Why? Someone, could you please, help me?

Average Session Duration

[sam8]

How are you calculating the average? With a table calculation, a measure, etc?

I'd need a little more context before I can say for sure what's happening.

[buenolcs]

Hi Sam, 

Thanks for trying to help me.

I just took those data and put in a excel spreadsheet and select all of them. Automatically the average appear on bottom. Example below.

"Média" means average.

[sam8]

I attempted to reproduce this internally, and I got the 6:17 as the average. Not exactly 6:18, but much closer than 4:39.

I must be missing something about your setup. Can you share more details about the field definition? For example, mine is defined like this:

[buenolcs]

Appreciate it, Sam! But the value i'd like to understand is 00:04:39 showed at Looker Studio when they calculate average, you know? What kind of math do i need to do to achieve that result. That's my setup.

Metric configuration:

Classify configuration:

BTW, i've created a table connected to my GA4.

[sam8]

That is super helpful! I think your screenshots pinpoint the problem. I think that the issue is the "Running Average" in the "Running Calculation" section of your first screenshot. I think that the grand total average is being applied to the average (not the running average), but the column values show the running average.

In my test, I turned on Running Average and now the numbers are larger:

I calculated the average of the second column's values and it's 00:14:52, not 00:06:17. So here the numbers are misleading. 

To test my theory, can you try changing Running Average to None and see if the average is correct then? My guess is that when you do that, all the numbers will get smaller and the average will be correct.

[buenolcs]

Here we can see a good comparison:

Example 1 - None

Example 2 - Running average

[sam8]

Thanks for sharing! It looks like the running average was not the problem.

I'm stumped! It's so strange that when I put those same numbers into a table, I get a grand total of 00:06:17, while you get 00:04:39. I don't see any difference in our setups.

Maybe someone else has seen a similar issue and can chime in with something we may be missing?

[buenolcs]

Thanks for your efforts so far, Sam. Apparently, to clarify this will be harder than I thought. It just makes me think about how accurate those data are (even in GA4).