A terrorist attack might seem like one of the least predictable of events. Terrorists work in small, isolated cells, often using simple weapons and striking at random. Indeed, the element of unpredictability is part of what makes terrorists so scary – you never know when or where they will strike.

However, new research shows that terror attacks may not be as unpredictable as people think. A paper by Stephen Tench and Hannah Fry, mathematicians at the University College London, and Paul Gill, a security and crime expert, shows that terrorist attacks often follow a general pattern that can be modeled and predicted using math.

Predicting human behavior is obviously a difficult thing to do, and one can’t always extrapolate from past events to predict the future. As one academic discussion of the topic points out, if you made a forecast in 1864 about how many presidents would be assassinated in office based on historical data, the expected number would be zero. But over the next 40 years, four U.S. presidents were killed in office.