Dr Robert Pape, a University of Chicago professor has done some quantitative analysis of suicide terrorism, and found the following:

I have spent a year compiling a database of every suicide bombing and attack around the globe from 1980 to 2001 — 188 in all. It includes any attack in which at least one terrorist killed himself or herself while attempting to kill others, although I excluded attacks authorized by a national government, such as those by North Korea against the South. The data show that there is little connection between suicide terrorism and Islamic fundamentalism, or any religion for that matter. In fact, the leading instigator of suicide attacks is the Tamil Tigers in Sri Lanka, a Marxist-Leninist group whose members are from Hindu families but who are adamantly opposed to religion (they have have committed 75 of the 188 incidents). Rather, what nearly all suicide terrorist campaigns have in common is a specific secular and strategic goal: to compel liberal democracies to withdraw military forces from territory that the terrorists consider to be their homeland. Religion is rarely the root cause, although it is often used as a tool by terrorist organizations in recruiting and in other efforts in service of the broader strategic objective.