Suppose that a group of 1000 college students were classified by sex (700 males, 300 females) and by class in school (400 freshmen, 300 sophomores, 200 juniors, and 100 seniors). If sex is independent of class in school, con¬

struct a contingency table showing all possible joint frequencies (such as:

the frequency of freshman males). Compare this with the frequencies which were actually observed: