What do we mean by a "healthy community"?

Question

In Is our community healthy?, labnut asked if our community is healthy. I'd like to make sure we understand what's meant by "healthy", though. Note that I chose to include "community" -- I like that reference in labnut's question, and I think it's important to understand the health of the community as being related to, but not covered by the health of the web site.

Answer 1

Is there any reason the stats at

http://stackexchange.com/sites?expand=true

can't suffice?

Also relevant are

• https://photo.stackexchange.com/users?tab=newusers
• https://photo.stackexchange.com/users?tab=voters
• https://photo.stackexchange.com/users?tab=editors

and of course

• https://photo.stackexchange.com/review

Answer 2

Labnut edited his original question to add a common definition of "healthy community":

a community evidencing growth, interdependence, and cooperation in a variety of areas. (Common usage)

Source: http://www.moricelakes-ifpa.com/glossary/index.html

This is a great place to start, but I think the real value for P-SE is to understand how these value statements are indicated and measured here. I'm actually a bit surprised I couldn't find a stock answer for this on meta.stackexchange.com, but the closest I found was one that talks about beta sites. Although the answers to that question explain why fixed numbers don't make sense across all the SE sites, I think that a "framework answer" could allow our community to evaluate its own health a little more precisely.

To that end, here are some metrics that we could conceivably watch over time (assume these are measured per month, or week-to-week, or month-to-month, or whatever -- just do it consistently):

• Duh, traffic. Very possibly too much of a macro measurement to be interesting, but I'd expect that we don't want to see traffic fall over something like a 3 or 6-month moving average.
• Total user count. Again, possibly not as important as more targeted metrics.
• Active user count. More interesting than total user count -- do we have growth in the number of people contributing?
• Average votes per question. Presumably, if we see this decrease, we've either got less activity on the site, or the questions are becoming less interesting (to large groups of people).
• Number of badges awarded (per x-time). This should remain steady or rise over time as the community grows, right?
• User "stickiness" - how to measure users coming back to the site frequently?
• Percent of users who are active / inactive (over x-time).
• Moderator turnover - same moderators == consistency (which is good), but also shows no new blood. Do we look for a small amount of turnover to keep fresh ideas flowing?

Note that I've taken care not to supply any specific numbers in any of these measurements; I think these need to come from community consensus, ideally. At a really high level, though, I think it makes sense that we don't want to see a really low activity level (indicating that the site has stagnated), and I think we also would be concerned about a huge spike in activity (which could lead to quality issues for questions and answers). I'd even go as far as to question whether absolute growth is really needed in order for us to consider ourselves "healthy".

In any event, I don't think there's a community platform in existence that's better able to monitor its own health than the SE platform -- as soon as we decide how we want to measure it.