Could you be more specific? What kind of effects do you want to measure? Casualties? Economic effects?

I would recommend Mohammad, Abdullah Y.S. (2005), “Roots of Terrorism in the Middle East” on its "Intensification of zero-sum terrorism cycle (IZSTC)”, or Jonathan Wilkenfeld's work for ICONS. However, I would see multi-variate analysis as Artur mentioned the question to be scoped more narrow. Terrorism in general or specific events, group or ideology based, effects in terms of targets/victims, resonance body, wider indirect reactions, sociological etc?

thank you Ivan Jascur for your valuable and precious comments.

There are different types of effects of terrorism. The effect I've been most interested is learning the conditions under which terrorism achieves its strategic goals (i.e., its stated political aims). A 12-year old seminal piece on this question is Max Abrahms, "Why Terrorism Does Not Work," International Security 31:2 (Fall 2006), 42-72. I largely agreed with him but raised a counter-example of 11 M. See "Correspondence: Does Terrorism Ever Work? The 2004 Madrid Train Bombings," by me and a co-author, International Security, 32:1 (Summer 2007), 185-192. Abrahms's response to our letter is part of this "Correspondence." By the way, in his subsequent articles on the topic, he now says that "terrorism almost never works."