In a short and bal­anced review of Con­nected–“a sci­en­tific look at the ties that bind us together”–we are treated to some inter­est­ing find­ings on social net­works and their myr­iad exter­nal effects–including how far these effects ‘travel’ through said net­works.

Con­trol­ling for envi­ron­men­tal fac­tors and the ten­dency of birds of a feather to flock together […] Chris­takis and Fowler found that we really do emu­late those we care about, whether we mean to or not. Being con­nected to a happy per­son, for instance, makes you 15 per­cent more likely to be happy your­self. “And the spread of hap­pi­ness doesn’t stop there,” they note. It radi­ates out for three degrees of sep­a­ra­tion, so that, say, your sister’s best friend’s husband’s mood exerts a greater influ­ence on your per­sonal hap­pi­ness than an extra $10,000 in income would. If he gains 50 pounds, it will be that much harder for you to stay slim, as the frame of ref­er­ence for what’s “nor­mal” changes through your net­work. Or, on the pos­i­tive side, if he quits smok­ing, your chances of kick­ing the habit improve, too, even if you’ve never met him. […]

Pub­lic health work­ers can more effec­tively stop the spread of sex­u­ally trans­mit­ted dis­eases if they know what kind of net­work they’re deal­ing with: a hub and spoke (e.g., a pros­ti­tute with many clients) or a more tran­si­tive “ring” net­work where peo­ple have few part­ners, but many of these part­ners over­lap (which could hap­pen at a small high school). On another front, they point out that vot­ing makes lit­tle sense for an individual—one vote never decides an election—but is far more ratio­nal in a net­work con­text. As with hap­pi­ness and obe­sity, the deci­sion to vote has reper­cus­sions through three degrees of con­nec­tions. […] Since lib­er­als and con­ser­v­a­tives tend to form their own social net­works, this means that your deci­sion to vote can increase the like­li­hood of hun­dreds of other peo­ple vot­ing for the same candidate.

I do won­der if these degrees of sep­a­ra­tion that exert influ­ence on us fluc­tu­ate with the size of each ‘degree’?