PT94.S2.Q16 - Heart Disease and Rat Sizes

Clemens_

Based on an examination of three types of rates (small, average size, and large), a recent study found that in rats, SIZE↑ correlates with HEART PROBLEMS↓. In other words, the study found that the greater a rat is, the less likely it is to have heart problems.

RRE EXCEPT. Four of the answer choices must be able to CONTRIBUTE to an explanation of this correlation; one does not. I did not do a pre-phrase here and went straight to the answers.

(A) Compared to large rats, smaller rats are more likely to have fatal diseases that strike earlier than heart problems. Under timed conditions, I took this to suggest: Small rats generally are more likely to die before heart disease strikes, so that heart disease will be overrepresented among the surviving small rats. However, this inference does not follow. If small rats tend to die young, the total NUMBER of surviving small rats that gets heart disease might be smaller, but there is no indication that there would be a corresponding increase in the PROPORTION of small rats that gets heart disease. This answer choice thus does not contribute to an explanation the observed correlation and thus must be right.
(B) Small rats are more likely to have blood vessel issues that causally contribute to heart disease. This helps to explain the correlation.
(C) Larger rats have less stress than smaller ones. If you assume that stress is causally related to heart disease, this contributes to an explanation. Under timed conditions, I thought that this assumption was too big of a jump, but compared to (A) this answer choice still is better. (A) does not contribute to an explanation at all, (C) does so if we make an additional assumption that seems fairly plausible from a common-sense perspective.
(D) The most common cause of heart disease in rats also causes them to be small. This explains the observed correlation by identifying a joint cause of small size and heart disease among rats.
(E) Larger rats do more exercises than smaller rats that causally contribute to heart health. This contributes to an explanation.

(C) is right, (A) is wrong. Under timed conditions, I had taken (A) to lead to a sampling bias making smaller rats not afflicted by heart disease less likely to survive such that heart disease becomes overrepresented among the surviving small rats. However, this inference is false. Just because small rats might be more likely to die for reasons other than heart disease, heart disease does not have to afflict a greater proportion of the surviving rats. I made a mistake here in assessing the implications of this answer choice and then switched to (C) because (C) requires an additional assumption to be explanatory ('Stress causes heart disease').

Takeaways: I originally had chosen the right answer (A) but then switched to (C) after mistakenly making the above-described inference. I likely was overthinking (A). I need to keep an open eye for the distinction between NUMBERS and PROPORTIONs. If unsure, close my eyes for a couple of seconds, do some deep breaths, calm down and reflect. I definitely felt uncomfortable in selecting my answer but could not quite identify what went wrong. NUMBERS vs. PROPORTIONs is a crucial distinction here, similar to e.g. POSSIBILITY vs. ACTUALITY, INATE vs. ACQUIRED, or MENTAL STATE vs. REALITY. Be vigilant, stay alert to these commonly used distinctions.