With virality continuing to be all the rage, whether it’s swine flu, happiness, or Internet services, it’s worth considering whether many things that seem viral actually are. Here is a 2008 BMJ paper on the subject that deserves wider attention:
Significant network effects were observed in the acquisition of acne, headaches, and height. A friend’s acne problems increased an individual’s odds of acne problems (odds ratio 1.62, 95% confidence interval 0.91 to 2.89). The likelihood that an individual had headaches also increased with the presence of a friend with headaches (1.47, 0.93 to 2.33); and an individual’s height increased by 20% of his or her friend’s height (0.18, 0.15 to 0.26). Each of these results was estimated by using standard methods found in several publications. After adjustment for environmental confounders, however, the results become uniformly smaller and insignificant.
Source: Ethan Cohen-Cole and Jason M Fletcher, “Detecting implausible social network effects in acne, height, and headaches: longitudinal analysis,” BMJ 337, no. dec04_2 (December 4, 2008): a2533.