In a yearlong study, half of the participants were given a simple kit to use at home for measuring the cholesterol level of their blood. ████ ███████ █████ ███████████ ██████ ██ ███████ ██ ███████ ████ ████ ███ ████████████ ███████ ███ ████ ████████████ ████ ████████ ██ ██████ ████ █████ ██████ ████ ███████████ ████ ███████████ ███████
In a randomly-sampled study of people with high cholesterol, why did participants with a cholesterol-measuring kit reduce their cholesterol more? Our job is to come up with a hypothesis to explain this phenomenon.
We're dealing with a pretty well-constructed experiment here, so we can be fairly confident it was actually the kit that made a difference. Our hypothesis might therefore take the form of a causal mechanism explaining how the measuring kit contributed to a greater cholesterol reduction.
Which one of the following, ██ █████ ████ █████ ██ ███████ ███ █████████ ████████
The lower a █████████████████ █████ ███ ███ ████ ████████ ███ ████████████ ████ ██ ███ ████
Even if the kit's accuracy can vary, how did having this kit help study participants to lower their blood cholesterol? (A) doesn't give us a causal mechanism or any other explanation of our phenomenon.
Participants with the ███ ████ ████ ██████ ██ █████ █████ ████ █████ ███████████ ██████
Hang on... participants with the kit avoided cholesterol-lowering foods? That makes no sense! This eliminates a possible explanation, rather than explaining anything. We want to know why participants with the kit had lower blood cholesterol, but (B) just adds confusion.
Participants with the ███ ████ ██ ████ ██████████ ██████ ███ █████ ███ ██████ ██ ███ ██████
But how did their use of the kit in these two months lead to a greater blood-cholesterol reduction? (C) still doesn't explain the link between the kit and lowering blood cholesterol.
All the participants ██ ███ █████ ██████ ████ ████████ ██ ███████████ ███████ ███ ████ ████████ █████████ ██████ ████ ████████ ██ ███ █████ █████ ███████
If this is true of all participants, what's different about participants with the kit that allowed them to lower their blood cholesterol more? (D) doesn't make any distinction between the groups in the experiment, so can't explain the different results.
Participants using the ███ ████████ ████ ████ ███████ ██████████ █████ ███████ ██ ██████ █████ ███████████ ███████
(E) gives us a causal mechanism linking the kit to greater blood cholesterol reduction: the kit encouraged participants in their efforts to lower their cholesterol. This explains why the study found what it found.