Formula
Sum of (First reply time - Post time) / Number of posts
How to measure
Timestamp every community post and its first reply, then average the elapsed time across a sample period.
Why track it
Fast community response time keeps a forum feeling alive and helpful, which retains both askers and the members who enjoy answering.
Example
A community team recruits volunteer moderators after average response time creeps past 24 hours, cutting it back down to under 2 hours.