Riots spread like viruses spread like “fake news.”

The American Council on Health and Social Science looks at the epidemiology of human behavior – and things we want to believe – by finding what riots, flu and “fake news” have in common:

Both actions and ideas spread like a virus; you need both an infectious idea and a receptive audience.

The metaphor comes from an epidemiologic model called SIR, for “susceptible, infected and recovered.” It describes the interaction of the infected with the susceptible. For this article, let’s ignore the recovered because rioters infrequently return for more rioting and we rarely change our opinions back to what we once believed.

R0 (r naught) is a measure of how contagious infection can be – how many individuals one person can infect. The value is based on the infectious period, the contact rate and the mode of transmission. In the case of rioting, the contagious period was the long-standing tensions between police and the community; the method of spread was social media, virtually instantaneous. R0 was principally the contact rate, and the researchers found that the number of rioters was related not to the absolute number of people already rioting, but rather to their density – how many there appeared to be. Fake news is similar, based upon long-standing tensions, disseminated instantaneously by social media, creating the information bubbles we share with our like-minded internet friends.

Transmission requires crossing a threshold – a critical mass must be present for patient one to become infected. An epidemic needs a critical mass of infected patients; one is rarely sufficient. In the French rioting, the threshold was crossed by seeing other people rioting. For fake news, the threshold is even more easily traversed. How difficult or time consuming is it to hit the Like or Share buttons? And with Likes and Shares you are responding to how popular it appears, not some absolute measure.

The R0 and susceptibility were sufficient to explain how the riot developed in any one area, but how did it spread across the country? Flu spreads from person to person; it is a contact sport. The closer you are to the source, the more likely you are to be infected. Rioting, as it turns out, is also a bit of a contact sport.

[via reddit]