Refer to Exercise 7.7 with Table 7.16 and the Spending data file.

a. Beginning with the homogeneous association model, show that backward elimination yields (CE, CL, EH, HL). Interpret its fit.

b. Based on the independence graph for (CE, CL, EH, HL), show that (i) every path between C and H involves a variable in {E,L}; (ii) collapsing over H, one obtains the same associations between C and E and between C and L, and, collapsing over C, one obtains the same associations between H and E and between H and L; (iii) the conditional independence patterns between C and H and between E and L are not collapsible.