A class having one attribute is known as the class of the first order, class of the combination two attributes as class of the second order. The total number of observations is denoted by N. Here, N is frequency of zero order, because it has no attribute to indicate.
(A), (B), (α), (β) are called frequencies of the first order, and (AB), (αB), (Aβ), (αβ) are called frequencies of the second order.
