Average Session Length (Mobile)

[HanzalahUssen]

whats the reasoning behind the First Launches being deducted from Launches in this calculation:

Total session length / (Launches - First Launches)

[Jennifer_Dungan · Accepted solution]

"Total Session length" is actually based the "Previous Session Length" in the Mobile SDK... so if this is the first time the app is launched, there is no "Total Session length" available. 

So let's break this out:

First Session

• First Launch and Launch event triggered
• Page A
• Page B

Session 2

• Launch event triggered
• Previous Session Length sent  (example 1:45)
• Page C
• Page D

Session 3

• Launch event triggered
• Previous Session Length sent (example 4:28)
• Page E
• Page F

Technically, 1:45 + 4:28 (6:13) should only be divided by 2, not 3, so "removing" first launches seems an easy way to do this... but technically, if that first launch was a year ago, and you are looking at this month, I am not sure how this would technically work... it sounds like an oversight on the math to be honest....

[scottcannon]

In regards to the issues with the math, if the first launch was a year ago then that first launch wouldn't be counted in the data for this month. From what I've read in the documentation this is a session level metric so any session outside your reporting window wouldn't be counted. 

Here are the details from this URL: https://experienceleague.adobe.com/en/docs/analytics/components/metrics/time-spent

Total session length, a.k.a. Previous session length

Mobile App SDK only. Determined the next time the app is launched, for the previous session. Calculated in seconds, this metric does not count when the app is in the background, only when in use. This is a session-level metric. Example: We install app ABC and launch and use it for 2 minutes and then close the app. No data is sent about this session time. The next time we launch the app, Previous Session Length will be sent with a value of 120.

Analysis Workspace, Report Builder, Mobile Services UI