Using our discussion of graphical models and collapsibility in Chapter 5, argue that when the true model is [123][24][456],

the test of marginal association for the u123(ijk)’s does not ignore any vital information. Is the same conclusion appropriate when the true model is [12][13][23][24][456]? What if the true model is [123][124][456], [123][24][456][15], or [123][24][456][15][36]?