How often does discriminatory questions get asked unintentionally?

Some poorly trained or ill-intentioned hiring construction managers will ask illegal questions. Eyeing an applicant's wedding ring, an construction interviewer might ask, “So you're married?” -– an implicitly illegal question. More likely, a question will cross into a gray area. Upon discovering that the construction interviewee went to the same university, another construction interviewer might ask, “When did you graduate?” Since age can often be inferred from the answer, a court or investigating agency might find illegal intent in the question.