Facebook and Reach

@Silona tweeted about an Economist article that talks about the max number of social connections a human brain can handle is about 150 (the Dunbar number). They interviewed Cameron Marlow, a researcher with Facebook that gave data on the average number of connections a person has on Facebook is 120. However, the people in the high network group are about 500.

The average male Facebook user with 120 friends:

• Leaves comments on 7 friends’ photos, status updates, or wall
• Messages or chats with 4 friends

The average female Facebook user with 120 friends:

• Leaves comments on 10 friends’ photos, status updates, or wall
• Messages or chats with 6 friends

The average male Facebook user with 500 friends:

• Leaves comments on 17 friends’ photos, status updates, or wall
• Messages or chats with 10 friends

The average female Facebook user with 500 friends:

• Leaves comments on 26 friends’ photos, status updates, or wall
• Messages or chats with 16 friends

So what does this mean for campaigns?

If we're looking at doing a branded Facebook application we'd probably see about 1000 users for a moderately successful app. So this lets us serve up 120,000 impressions on the status updates or about 840,000 impressions per week. [Note: As of last year when I checked, Facebook allows applications to send out 7 updates per week].
This level of engagement is pretty low as status update, the number of users that are active in that range is about 5.8% so you're probably getting a number closer to 50,000 real eyeballs on your brand.
So next time you do a media spend, take a look at how much it costs for getting your impressions on to Facebook and maybe the cost will justify doing an application instead.