I understood that people were asked beforehand about their beliefs. Afterwards would indeed be silly, and I would have been very surprised if 60 years of peer review would not have caught that.

Just checked the two links I pasted earlier. The second link (skeptics dictionary) quotes:

    The expression dates back to 1942 and Gertrude Schmeidler, 
    a professor of psychology at City University of New York. She 
    asked her students whether they believed in psi *before* 
    giving them an ESP card test. 

So your explanation doesn't hold here. People were asked first, and then tested.