Formula:
H0:there is no association between the two categorical variables of interest
χ2 = Σ ((Oi - Ei)2/Ei )
For each category,i,of k cells there is an observed frequency, Oi, and an expected frequency, Ei
(1) difference between Oi and Ei small,
χ2 is small, and H0 may not be rejected
(2) larger
χ2 may be large, and H0 may be rejected