OK. I think overnight I figured this one out, or maybe I forgot all the relevant details - not sure which:
42. heart disease and doctors – preexisting heart disease condition v. nonvitamin
Here's the thing ... it was a weaken question, and the conclusion was something like, "It must have been the vitamins B12 or whatever that were associated with lower degree of heart disease."
OK ... the non-vitamin dietary question weakens this, because they are making the explicit claim not only that these women had lower incidence of heart disease, but it was because they had higher dietary intake of B12. If foods that have B12 also have some heart disease lowering thing in them, it is POSSIBLE that the conclusion is not justified, thus it is weakened.
BUT...the preexisting heart condition one is actually a strengthener ... not a weakener, because the conclusion is about a LOWERED risk of heart disease. If the women in the study had a lower incidence of heart disease (and we know they had higher intake of B12, from the stimulus) AND they had a preexisting condition, that would make the apparent effects of B12 that much more amazing, not the other way around...
Just my $.02 ... maybe I forgot a critical piece of the question when I woke up at 2AM thinking about it.
I do not believe you are correct. You're assuming there was no control group in the study. You can't compare one group to itself. In order to conclude that the increased B vitamin intake lowers risk, the researchers must utilize comparative data from a control group that does not have an increased level of vitamin B intake. The women in the study
did not have a lower incidence of heart disease...rather, the women in the study who had greater intake of the vitamins
had a lower incidence of heart disease. So I do not believe that the preexisting condition answer is actually a weakener. Any "amazing" effects of B would not be observed for every human within the scope of the research...only to the group we identify as B vitamin beneficiaries, a group that may only exist because they were the only ones in the study who did not have preexisting heart conditions.
How can you conclude on the risks of developing heart disease for a certain group if your subjects may already have heart disease before the study begins? How do you differentiate between the effects of the vitamins and the random luck of the draw of unknowingly selecting for your test or control group a patient that came into the study already with heart disease? To me, this seems like such a weakener that we don't even have to debate the issue of whether the stimulus mentioned how the vitamins were administered to the subjects (and I am sure that it didn't, a detail I double checked). I'll bet the house, farm, and accompanying silo on the already had heart disease answer choice.