Here is an interesting article by two British scientist, R.A. Hill, and R.I.M. Dunbar. "Social network size in humans.” It was published in Human Nature 2003, 14:53-72. They looked at social networking in Western society through Christmas card exchange. They were following up on some neurological work that implied the human brain, because of the cortex size, might limit us to the ability to actively handle about 150 close relationships at any one time. The authors claimed that their work supported this contention.
They found that each household sent out an average of 68 cards to an average of 153 people (as some cards went to more than one person). I may be missing something here but to me it just means that white Brits (the sample) send out a lot of Christmas cards. It takes a great leap of faith to imply that this cultural act correlates with the closeness of recipients. There are probably many differing criteria for sending out cards. I am always amazed at some of the cards I get. Based on my own experience, I would not correlate degree of closeness with probability of receiving a card from someone. If anything, there may be a negative correlation with the exception of my relatives.
I wonder what other experimental situations can be mined here. Perhaps your email address list? What about your blog roll? But there are many reasons people get on each of these lists. I recently got a Linked In request from some guy who called himself “I am your linkedin daddy” with over 6,000 “close” connections. I wonder how big is his cortex? I declined but it appears that he got a lot of people who will accept any invitation to be connected. Perhaps he wants to sent up a “match.com” type service for linkedin junkies.
How many active relationships can you manage at one time? Intuitively I think the number 150 is perhaps right but I would not base this on Christmas Card behavior. Of course, this means you have to find 150 people who want to be connected to you.
Thanks to Valdis Krebs for sharing the link to this work.
Bill, this is very interesting. Valdis may remember where this comes from: There are reported to be 25 people who consistently remain in our networks throughout our lives. The number here strikes me as very large and a by-product, as you say, of a particular social custom rather than intimate relationships.
Posted by: Jessica Lipnack | January 18, 2006 at 01:45 PM
Another thought on this number of 150. It's the typical point at which organizations create another unit or another level or another building. Bill Gore of WL Gore never let more than 150 people work in the same building.
Posted by: Jessica Lipnack | January 18, 2006 at 02:29 PM
Jessica - Thanks for your comments. Does anybody know any more studies on this number? I wonder if people from large extended families have more capacity for other extended networks. It might be 25 from "strong ties" and 150 for weak or perhaps "semi-strong ties."
Posted by: Bill Ives | January 18, 2006 at 02:40 PM
"Does anybody know any more studies on this number?"
Not necessarily more studies but certainly I have heard that number before and it is widely mentioned in "The Tipping Point: How Little Things Can Make a Big Difference" (Included the link from Amazon but somehow the preview cuts it off). Here is a quote from the book:
"Keeping things under 150 seems to be the best and most efficient way to manage a group of people. When things get larger than that people become strangers to one another". Bill Gross, leader of Hutterite community. (Hutterite policy is to split before a group reaches 150)"
Also it is mentioned in some of the reviews from the book itself (To be found as well in the same linke from Amazon I mentioned above), in case you are interested in reading some more.
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Here is the link to the book in Amazon and the reviews: http://www.amazon.co.uk/exec/obidos/ASIN/0349113467/qid%3D1095238029/sr%3D1-1/ref%3Dsr_1_3_1/202-8724656-5599845
Posted by: Luis Suarez | January 19, 2006 at 08:18 AM
Luis. Thanks for your comments and the additional data points on the 150. So perhaps there is some universal here. Like the magic number 7 plus or minus two in terms of the numbers we can actively remember. I recently did a review of Blink, Gladwell's most current book. You will find a link to it if your scroll down on the right side to recent articles.
Posted by: Bill Ives | January 19, 2006 at 08:55 AM
Luis - I followed your link and see that you also write about knowledge management so I added a link in my blog listings. Look forward to reading more.
Posted by: Bill Ives | January 19, 2006 at 08:56 AM
You are most welcome, Bill ! I have meant to weblog as well about this "magic" number of 150 since I have got some additional information that I am currently trying to shape up for an upcoming weblog post but I can certainly agree with your comments about how extensive that 150 number could be to other social groups and maybe not just communities per se. Thus I may go ahead and blog about it in my weblog at some point. By the way, thanks a lot for the headsup and for the addition to your blog listings. Oh, and for the lovely reading on your review of "Blink". I haven't got my hands on the book yet but your review would be a nice start before I get my hands on the book itself. Thanks again !
Posted by: Luis Suarez | January 19, 2006 at 02:12 PM