Sunday, February 15, 2009

The Point-Source Epidemic in Facebook

Billy, being a touch behind the technology curve, came to Facebook at just about the same time that he began to blog (i.e. a bit less than two months ago). One or two friends had long advocated that he check it out, but he resisted, highly skeptical of what he considered an online exercise in frank narcissism, until he succumbed to peer pressure and joined. Since then he has been he has been mildly pleasantly surprised to see names and faces of long-gone friends from high school, college, medical school, residency, and other odds & ends of life and to find out what's going on in their lives, see pictures of their spouses and children, and exchange short notes about where life has taken us. Although I already spend far less time on it than I did one month ago, it's been unexpected fun.

But there are limits, and anyone familiar with the Facebook culture, particularly those who actively use the website, will not be surprised to know there is indeed a heavy element of navel-gazing that goes on. Facebook invites participants to tell their friends "What are you doing right now?" and several users appear to be delighted by noting that they are "about to go to sleep," "wondering what to drink tonight," or "loving Sudafed today"--apparently considering such pronouncements critical for posterity.

One such activity that has been making the rounds of late has been the Facebook equivalent of a chain letter. Dubbed "25 Random Things People Don't Know About Me," the game is to write little pieces of trivia as the title suggests, then "tag" 25 other Facebookers who are encouraged in turn to submit their own lists. While Billy has enjoyed perusing some of the lists, he has remained reticent to share the things people don't know about him as there is likely a good reason they don't know such things.

Nevertheless, "25 Things" has been a sensation of late, earning the attention of such trendspotters as Slate and NPR among others. The Slate article discusses the evolutionary origins of the concept; apparently, "25 Things" had several prior incarnations before the current version took off. Readers familiar with the concept of the cultural meme will find all of this familiar, but one fascinating observation about the popularity of the list concerns the kinetics of its spread. Earlier, Slate had asked its readers who had posted their own "25 Things" list to send in the date of when they were first "tagged," and when they subsequently posted their own lists. The curves (which I am having a terribly difficult time pasting here) look exactly like this:

This graphic describes what's known in the biz as a point source outbreak, and this particular graph shows cases of cholera after a population drinks a single source of contaminated water. The mathematical description goes like this: "the epidemic curve in a point source exposure commonly follows a log-normal distribution, in which the number of cases increases rapidly, reaches a peak, and then gradually tapers off, creating a right-skewed curve, or a curve in which the mode (or highest point of the curve) is shifted to the left of center."

The Facebook "outbreak" of "25 Things," therefore, appears to perfectly mimic a human infectious disease epidemic at a population level.

A certain caution needs to be applied in interpreting the Slate data. The participants were all, of course, Slate readers, which is pretty clearly a self-selected audience (I would guess older, more well-educated, and more likely to be white-collar relative to the average Facebooker) and could represent a serious confounder to the "study," such that there was no genuine point-source epidemic if you look at the overall Facebook population. Plus these are only voluntary respondents; we might not have heard from readers who decided to post their list either well before, or well after, the "outbreak" which occurred around January 30, and again that would change the kinetics of the epidemic and the curve might not match the one above. Still, at least for this subgroup, I find the data compelling. Art does imitate life!


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