Terrorism is not about terror
Biggest problem with analyzing terrorism is in the definition.Classifying both Hezbollah and al-Qaeda as terrorist groups means that you have spread the definition for any group that may have bombed civilians at some time or another. I would claim that Hezbollah is much more than terrorist group. Their success or failure does not depend on terrorism.Second bias might be exclusion of successful terrorism that is later legitimized. For example, are IZL and Stern Gang included? I would say that they were highly successful. How about Stalin and early communists in Russia? If terrorists have enough support and are successful early, terrorism turns into ethnic cleansing and/or revolution and it is taken out from the list.Third problem is that terrorism seems by definition be the underdog because official or state terrorism is excluded. Many dictators use terrors successfully as  tactics (kidnapping, torturing and killing civilians or relatives of their opponents) but this does not fit under terrorism. Taiwans  White Terror or Augusto Pinochet used terror as tactics but it's not classified as that.