How to Use the “Network Density” Formula to Measure the Health of a Community

How can you determine the health of a community?

A lot of community managers just go with their gut on this one, or use proxy metrics like signups, posts per day, klout scores, retweets or some other metric that is fairly hollow, but there are better ways.

This is very much a work in progress, so I’d love to collaborate. If anyone has any thoughts, please jump in the comments sections and let’s discuss. That being said, most of this isn’t new, it’s just stolen, adapted and generally simplified from concepts like Network Theory, Affinity Groups, Clustering Coefficients, Small World Networks, and other things I will never fully understand or convince people to invest tech into.

Let’s dig in…

What is Network Density?

First off, Network Density (ND for short) isn’t one number, it’s more like blood pressure where they say “80 over 120”. I have no idea what the 80 or the 120 mean, but it works as an analogy. So, with that in mind, ND breaks down roughly as:

Average Distance Between Users : Number of Paths : Frequency of Interactions

or simply put…

AD : NP : F

Lets break each part down…

Average Distance Between Users (AD):

This is known as a small world network problem. It’s also been called the “average shortest distance”.

You want this number to be low.

Simply put, it’s the number of “hops” it takes to link one person to another. Think of it as the six degrees of kevin bacon – anyone is probably connected to anyone by some number of steps.

Generally the fewer the steps between 2 arbitrary people, the closer your community is and the easier it is for people to jump into new conversations.

For example, Bob starts a convo, Mary knows Bob and replies, Sam knows Mary so can jump in, and John knows Sam so he jumps in as well. John never knew Bob, but is now engaging with him because of your community connections.

The fewer people it takes to connect John and Bob, the better you generally are and the lower your AD will be.

In social networks this is easily defined as “friending” or “following”. In forums or gaming it’s a little more complicated, but you can use private messages, public replies, shared threads, guild or clan membership etc. Define it and play with it as is most useful to your community.

But, just because you have a low AD, doesn’t mean your community is healthy. You have to think about the health of the connections, so we add in the Number of Paths metric.

Number of Paths (NP):

You want this number to be high.

Having lots of backup connections is good. If you removed a key person from your community, what would happen? The more ways you can get from Person A to Person B, the less impact that loss would have.

In the earlier example, John and Bob connected with each other through the “path” of Mary and Sam.  If you took Mary out of the community, you’d need a new path to connect John and Bob.  The more of these backup paths, you have between your community members, the better.

But, just because you have a low AD and high NP, you could still have a low engagement community, which may or may not be “good”. So we take Frequency of Interactions into account.

Frequency of Interactions (F):

You want this number to be high.

My extended family is rather large, has a low Average Distance between any two people and a high Number of Paths between us (we all know each other and can reach each other in multiple ways)…but we don’t really talk all that often.

Is that a healthy relationship? It’s strong, but over time without many interactions, it really isn’t going to maintain it’s strength and resilience.

Think about your high school group of friends – low AD, high NP, but as soon as you all left school the Frequency of your communication might have dropped and the group became weaker.

The important part here is that it’s not absolute, it’s very much relative to your situation.

A community of 100 people with 10 total interactions may be “better” than a community of 1000 people with 100 interactions. You need to pick the right metric and scale for you and your goals.

Also, pick a time frame that works for you (interactions per day, week, month etc) and define what makes “an interaction” the way that is most meaningful to your goals.

And just to throw a wrench into the works, if you can, try to take quality into account (long, positive, substantive comments).

So, We Have the Formula… Now What?

This formula gives you a baseline.  You can then track how your community is doing based on how that baseline changes.

Watch the change, not the number.

As with all metrics, the numbers themselves don’t really matter….it’s the direction of those numbers over time – Is AD generally going down while NP and F are generally going up. Are the numbers generally reflecting or indicating the changes you’re expecting or working towards in your community, etc.

There’s not really a “right” combination or single number that you should aim for. And it’s confusing as hell when you first measure…”What on earth am I looking at? Is this good????”.

F is fairly easy to understand, but AD and NP really confuse a lot of people. Is 4 : 10 good, or should it be 1 : 10000? To be honest, I’ll be damned if I know 🙂

Globally we’ve all heard of the “six degrees of separation” where AD=6, amongst movie actors the AD=4.54, and Facebook users are between 3.74 and 4.72 depending on the source. So, as a benchmark, below 10 and above 2 are probably “ok” but I’m just guessing, the “real world” seems to be around 4 or 5.

For NP it’s harder, partly because you can manipulate it – If you have AD of 3, then your NP might be 4. If you increase your AD reporting to 4 (remember higher AD is worse), there are LOTS more paths – it should follow a power-law distribution (I think).

To start, you can try tracking 2 “hubs” and see how the NP changes over time, you can take the AD at a set point in time as your benchmark (in money we often hear “$10,000 in 1990 dollars, same thing) or set an arbitrary AD number – “how many ways are people connected in fewer than 27 hops”.

Again, you have to apply it to your situation and use whatever makes most sense for your goals and needs.

Network Density will be Different Based on Community Types

Different platforms and different goals also lend themselves to very different Network Density numbers.

For example, a broadcast account on Twitter that has 3,000,000 followers might have an ND of 2 : 1 : 300 because every user is connected to every user through the broadcast account (AD=1), ONLY the broadcast account (NP=1) and people tend to reply to or RT it giving it a high(?) F.

Number of Paths=1 isn’t a problem because, for a broadcast account, when they are done with broadcasting it doesn’t matter if the followers continue interacting. Here, the most important metric is going to be F.

If I saw an ND of 2 : 1 : 300 in a community, the NP=1 would REALLY worry me and I’d say you really don’t have a community. But for broadcast or social, this is probably what you will see.

A gaming community, however, might have an ND of 4 : 300 : 2 because they’ve chosen to implement a guild system and count everyone in the guild as being connected. Not everyone in the guild talks to everyone else every day so F is low, but anyone in that guild could reach anyone else at almost any time (within 4 hops) if they needed…and anyone could be booted out from the guild without having a major affect on the health of the guild or the community.

As your Community Grows, Network Density will Change

The life stage of your community is generally also going to affect your ND.

Early stage communities almost always have a very low AD, an NP relatively high compared to their userbase, and a really low F. There just aren’t that many people (AD = low) and they all probably know each other (NP = high), but this probably isn’t their primary communication path just yet (F = low).

Growth communities are generally going to see a rapid increase in AD and drop in NP as a lot of strangers enter. This is natural and probably “ok” as long as the rate at which it is happening isn’t too high and the old-timers can connect to the new-timers fast enough to pass on the culture you spent so long building. The cool part is you can see this dilution happening and can take steps to address it, something you might not see or act on based on registered users or comments per user alone.

Mature communities are generally always going to have a high NP and F, because there’s just so much “stuff” going on. Here you may want to adjust the scale to your userbase size at some point – an F of 1,000,000 isn’t a particularly useful number, so finding other ways to track changes more granularly might be helpful.

Moving Forward…With Your Help

Here’s the best part, I have no idea how you’re going to gather the data to calculate these numbers. If anyone wants to be entrepreneurial and charge us all copious amounts of money for an easy solution to gathering this information…please let me know, I’d love to join that party 🙂

I’m genuinely interested in getting input to improve this thing, there are a lot of complications, nuances, sub networks and outliers when you start looking at network in this way, so please jump in the comments and help refine.

I’m clearly stumped on how to generalize frequency, particularly how you take quality into account and how to give it a meaningful definition – is it average frequency along your Average Shortest Distance, is it between a set group of people or set size, is it a direct calculation of all interactions with some amazing algorithm that sits on top of it (and if so, what is that algo), etc.

I don’t know, and would love help!

Oh, and Standard Disclaimer:

I do not claim to have thought of everything, for every situation, nor do I intend to. These things worked in at least one situation and are not guaranteed to work everywhere. Individual results may vary. There is no substitute for experience and timely, intelligent decision making. This discussion is designed to explore several aspects of community which, when used collectively, could produce positive results. (Disclaimer borrowed from Ray Land)

Enjoy this article?

Enter your email to receive free community management advice in your inbox:
About the author

Justin Isaf

Justin is a community management consultant. He founded Communl which mentors and trains in-house community managers to make them more awesome. He has been doing the community management "thing" since 2003, which has including everything from launching communities from scratch to running the largest actively managed community on the interwebs.


  1. […] How to Use Network Density Formula to Measure Health of a Community 1 Upvotes Discuss Flag Submitted 1 min ago Jennifer Sable Lopez Community Comments […]

  2. […] are doing some really great work on measuring community. Reading the comments on articles like How to Use the “Network Density” Formula to Measure the Health of a Community shows a real desire for quantifying […]

  3. […] Originally posted at […]

  4. […] and David Spinks are doing great work on measuring community. Reading the comments on articles like How to Use the “Network Density” Formula to Measure the Health of a Community shows a real desire for quantifying […]