I looked through to see which people I haven’t heard from, sometimes checking their profile to see if they said anything in last 2 weeks. Then unfollowed them if it appears they are not around anymore. I was left with fewer people I follow obviously so that’s the fraction. I’m probably a small sample size though my guess is the wider network drop off rate is much higher - at least 35% maybe up to 50. But I’m totally making these numbers up.