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  • One of many problems with survey research in general is that you can only survey the survivors. In other words, if you were to do a survey of people who were known to have played Russian Roulette and you sent out the questions before the time they were going to play and then you come back six months after they played Russian Roulette, you would probably discover that among the people who did come back there was no harm done.

    "Do No Harm: An Interview With Thomas Sowell". Interview with David Harsanyi, thefederalist.com. January 13, 2015.