In the spirit of previous retrospectives, here's one from Los Angeles.

Last Wednesday, we had our 52nd consecutive meetup. This is noteworthy, I think, for a couple reasons:

• We do weekly rather than the more common bi-weekly or monthly meetups
• We suffered from a long period of near-zero attendance after most of our core members left to fight the good fight with MIRI in late-2015 to early-2016

Here are the things that may have contributed to the success:

• I "rebooted" the meetup when Scott announced SSC Meetups Everywhere. This was an excellent Schelling Point which brought back a lot of older members and also many newcomers. We had ~22-24 people show up over the course of the night, which was a little overwhelming even given the spaciousness of our location. There were probably 5-6 conversations going at any given point. The breakdown was ~10 regulars and 12+ newcomers. 2 of those newcomers became consistent regulars and a few others showed up at least one more time. (It's worth noting that the new regulars have nearly universally been people who live close to the meetup - Los Angeles is a big city and transportation sucks!)
• Topics! Having topics seems to be very important, even if the focus given to them at the actual meetup is minimal (we do always discuss the topic, but there's no rigid structure/schedule, and for the most part conversation flows naturally).
• Social bonding. Post-reboot, the focus of the group changed from "we're here to discuss this topic and interesting insights related to it, or to learn something new" to "we're here to hang out with people who, in general, think this is an interesting topic, but we have lots of other stuff to talk about too". Many members of the group also started spending social time with each other outside of the meetup, including throwing semi-regular parties and traveling together.
• Reliability. Knowing that a sufficient number of people will be at the meetup is a strong motivator for both regulars and newcomers to attend. Obviously this is hard to bootstrap, but the reboot and Topics! both factored into this. Our smallest group size (near a major holiday) was 4 people, and our largest (excluding the first one) was ~14. 8-10 is the more usual number. As the organizer, I have made a point of attending every meetup. It's fairly fortunate that all of the year's illnesses missed Wednesday!

Here are things that could use improvement:

• Location. We meet in a wine bar next to a movie theater in a fairly large mall. The upsides are that it has a lot of space, they don't require that we spend money (though a few people do buy drinks/food), and they don't mind if we move the chairs around as long as it isn't too crowded. The downsides are that it plays somewhat loud music, and gets even more loud when it's busy, it hosts events sometimes which drastically cuts into our seating capacity and sometimes schedule, and the food is mediocre (charitably). I made one attempt to change locations a few months ago. It wasn't catastrophic but insufficient planning/vetting led to a somewhat poor choice of venue, so we stayed at the current location. In general, moving seems like a Hard Problem for several reasons.
• Leadership. I was extremely lucky with how things fell together, and coming up with a topic every week, occasionally organizing parties, and nudging people until they RSVP so that those parties actually happen are tasks that aligns pretty well with the kind of organizational skills that I have, along with showing up to places on-time and reliably. Other tasks, like investigating new meetup locations, take more time and more energy. I have unsuccessfully attempted to find somebody to share the joys and horrors of leadership with, both to grow the community and mitigate the single point-of-failure mode.
• Growth. We do have a slow accretion of new members, but it's entirely passive - apart from posting weekly announcements, I do no active advertising. Our retention rate for new members is low (maybe 15-20% become regulars) but I'm not sure how far away that is from baseline, and it's fairly prone to large swings given the small numbers involved. For now, the location seems to be an intractable problem - more than half the group lives or is moving to the general area, and moving the meetup to a more central location in the city would be a significant - perhaps deadly - cost. Moving the meetup to another location in the same area solves other problems but not this one. Similarly to Leadership, the skills involved in growing the meetup are both heavily time-consuming and weaknesses of mine.

Other stuff:

• You may notice that the weekly aspect of this meetup isn't in one of those two lists. It has upsides (faster social bonding) and downsides (less urgency to attend and/or greater time commitment), and I think the final judgment of whether it's a good idea strongly depends on local factors.

I hope this is helpful/interesting, AMA. Advice along the "could be improved" fronts is appreciated.