
16 Bayesian Networks: With Examples in R
where we denote the categories of Travel with t ∈ T, the categories of Edu-
cation with e ∈ E, and the configurations of Occupation and Residence with
k ∈ O × R. Hence, n
tek
is the number of observations for the combination of
a category t of Travel, a category e of Education and a category k of O × R.
The use of a "+" subscript denotes the sum over an index, as in the classic
book from Agresti (2013), and is used to indicate the marginal counts for the
remaining variables. So, for example, n
t+k
is the number of observations for t
and k obtained by summing over all the categories of Education. For Pearson’s
X
2
,