Which of the following is true with a voluntary survey when compared to a mandatory census?
A) A sizeable proportion of people do not answer such surveys. B) If people refuse to answer at random, then non-response would not cause a problem; we just would not get as large a sample. C) We would expect more variation in the mean incomes we calculate, but they would not be systematically different from the population mean. D) A), B), and C) are all true.
E) A), B), and C) are all false.