At the most elementary level, science begins with counting things: atoms, earthquakes, distance from the earth to the sun, or even worldwide terrorist attacks. It seems clear that we cannot do a very good job if we cannot first count how much of it there is.
LaFree, Gary. 2013. Lone-offender terrorists. Editorial Introduction: Loner Attacks and Domestic Extremism. Criminology and Public Policy 12: 59-63. http://onlinelibrary.wiley.com/doi/10.1111/1745-9133.12018/abstract