The highest percentage of respondents—17 percent of those who wrote a note—composed their missive the same day they were first tagged. The numbers decay from there, and the median value is three days. Meyers found that this too was best described exponentially, though the figures decline instead of increase over time. You can think of it like radioactive decay. In the same way that, say, Thorium-231 atoms have about a 50 percent chance of decaying each day, regardless of how many days they've been around, people tagged in a "25 Things" note do not become more or less likely to participate as time passes. Meyers does note, however, that these calculations do not factor in individuals who choose not to participate or have yet to do so.
Why does it appear that the "25 Things" fad has died out? One could argue that a selection bias in Slate's data are exaggerating the decline, as those who haven't yet encountered the meme are likely underrepresented. I don't think this is the case, though. As we see in Fig. 3, most people write their notes within a week of being tagged for the first time. The decline we see in Figures 1 and 2, then, is likely legitimate: Because the fad peaked more than 10 days ago, it's unlikely that there is a large number of people who've been tagged who are still waiting to write their own note. My guess is that, like a Ponzi scheme, "25 Things" fizzled as soon as Facebook ran out of willing participants. Anecdotally, there don't seem to be a lot of people left who are sitting around, waiting to be tagged.
All in all, Facebook infections look remarkably similar to human ones. And like organisms, the odds do seem stacked against all but the fittest of memes. The "Notes" application—including the ability to tags friends—has been a feature of Facebook since August 2006, a Facebook spokeswoman told me on Tuesday. (The PR rep also confirmed that Facebook itself had no part in sparking the trend.) The fact that it took two-and-a-half years for a Notes-based meme to hit it big suggests long odds.
Still, viral marketers might take note of the patterns that "25 Random Things About Me" obeyed. The best hope for someone looking to start a grass-roots craze is to introduce a wide variety of schemes into the wild and pray like hell that one of them evolves into a virulent meme. If evolution is any guide, however, there's no predicting what succeeds and what doesn't. Just look at the platypus.