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Friday, November 20, 2015

Memes, Syrian Jelly Beans, and Risk Assessment

Terror, refugees, and flawed intuitions

A meme going around compares Syrian refugees to jelly beans:

If i gave you a bag of 50,000 jellybeans and told you 100 are poisonous, you wouldnt accept them right? Then why would we accept 50,000 refugees if some of them are bad?

I like jelly beans and numbers so I did a back of the envelope calculation. In the US there are about 15,000 murders per year. Most murderers kill only one person. Even serial killers kill only 2.8 people on average. Thus, 15,000 is also approximately the number of murderers in a year.*

Let’s say that people live on average for 50 years — that’s low, but our figure for the number of murderers was a bit high — this means that in the current population there will be approximately 15,000 * 50 = 750,000 murderers.

750,000 killers among us struck me as an awful lot when I first calculated the number, but there are approximately 166,700 people in prison for murder right now, and of the 750,000, some of them are not yet murderers and some of them won’t be caught. Thus, on reflection, 750,000 seems like a scary, yet reasonable estimate.

The current US population is 322 million, so there are .0023 murderers per capita, or 2.33 murderers per 1,000, or 116 murderers per 50,000 people in the United States.

Put differently, about 116 American babies out of every 50,000 will grow up to murder someone. (Perhaps the NYMag should rerun its poll?). In contrast, only 100 of the 50,000 jelly beans were poisonous.

Thus, if anything, Syrian jelly beans look pretty good compared to American jelly beans.

Addendum: See Alex Nowrasteh for calculations going beyond jelly beans.

This post first appeared at Marginal Revolution.

* Ed. note: In the last five years, according to the FBI, the average number of murder offenders each year is 14,450. Current average life expectancy at birth is 78.

  • Alex Tabarrok is a professor of economics at George Mason University. He blogs at Marginal Revolution with Tyler Cowen.