"It was pre-existing baseline LDL-C changes and not during study LDL-C changes that separated the two subgroups."

Well, the question of compliance may still factor into the initial stratification.  Study participants who were poor at taking their statins might be expected to be concentrated in the high LDL group at the start of the study.  And if they continued in their noncompliant ways during the trial, perhaps taking both their statins and their apabetalone infrequently, it is no surprise that that taking apabetalone (but not really) would find you faring no better than the control group.

Jupe