An economist concluded that Kregg Company deliberately discriminated against
people with a history of union affiliation in hiring workers for its new plant. The
economist's evidence is that, of the 1,500 people hired to work at the new plant,
only 100 had ever belonged to a labor union, whereas in Kregg Company's older
plants, a much higher proportion of workers have a history of union affiliation.
Which of the following is an assumption on which the economist's argument
depends?