According to this, there are only ~50,000 reported cases of CSA in the UK, while there are 800,000 cases (1/20 of 5-19 year olds). This gives us a current reporting rate closer to 6%.
I guess it depends on the reason they’re isolated. And the more “expensive” interventions in terms of inconvenience to regulars should be weighted by the excepted gain. A proxy for that might be the number of isolated EAs.
Examples of interventions would be diversifying meetup times/locations if it’s due to time/location conflicts. It might be easier to test this by adding online events and comparing the number of new attendees.
Marisa mentioned that 1-1’s (with the organizers or other members) would also be beneficial and would reduce the awkwardness of joining a meetup where everyone but you knows each other.
Another idea might be to sponsor local groups by providing support or training, like how (I imagine) EA Philippines does to their local chapters. But seems easier for a country group to do this to a city/uni group, rather than a city group “sponsoring” another city.
This was the only one I thought of. I will be interested in hearing about the intervention if you're willing to share. Good luck regardless!