This is how they did the randomization (in which I am interested more):
For the study, three economists interviewed 1,600 Pakistanis, half of whom had been on the hajj in 2006 and half of whom had applied for visas to go but were rejected. Respondents answered 200 questions in face-to-face interviews that lasted hours. The interviews took place five to eight months after the pilgrims came home.
And this is the result:
Muslims who undertake the hajj "return with more positive views towards people from other countries," are more likely to say "that people of different religions are equal," and are twice as likely as other religious Muslims to condemn Osama bin Laden, the study found.Looks like economists can now have job opportunities in the Ministry of Religion...