It may not have occurred to the researcher but Iranians aren't Arabs (neither for that matter are Asians and SE Asians or Sudanese etc. which may answer Dave’s query) The extremist religious position of al Qaeda is essentially underwritten by Arabism.
I have found a site with deaths of al Qaeda operatives killed in Iraq up until June 2005. Having a bit of trouble authenticating the figures but will post when I do.
It shows deaths from many nations including three from the Sudan. But the overwhelming number comes from Saudi Arabia. The question to ask is, is that because of the US presence (not there now?) or the pervasiveness of the Wahhabi fundamentalist religious philosophy in Saudi Arabia.
Suppose the researcher is right (he is dealing with statistical correlations not causal relationships) then an important question to ask is why do the Saudi, al Qaeda operatives object to the US presence in the "Holy Land"? We don't have to guess they have told us. Because of the holy cities of Medina and Mecca where infidels are forbidden. Thus we are back to a religious reason with political undercurrents
