Bunuel wrote:
Thirty years ago, deer and elk in selected parts of the Rocky Mountains were first discovered with a condition known as wasting disease. In 1970, two percent of the deer and elk killed by hunters were diagnosed with the disease. In 1995, that percentage had grown to six percent. This increase in the incidence of the disease proves that wasting disease has become much more prevalent in the last twentyfive years.
If true, which one of the following selections most seriously weakens the author’s conclusion?
(A) Wasting disease has not been discovered in domestic livestock or in moose or bighorn sheep, which are also found in significant numbers in the Rocky Mountains.
(B) Wasting disease tends to make deer and elk lethargic, making them more easily killed by hunters.
(C) Since it was first reported, wasting disease has occasionally been diagnosed in deer outside the Rocky Mountains.
(D) Hunters have grown more reluctant to cooperate with the authorities in reporting their deer and elk harvest, because if wasting disease is diagnosed in their harvest, the meat will be destroyed.
(E) It is very difficult to diagnose wasting disease more than twenty-four hours after death, so many cases of the disease have gone undiagnosed.
The disease was first discovered 30 years ago. Around that time, the incidence was 2% among those killed by hunters.
Now, the incidence is 6% among those killed by hunters.
Say there are 1000 deers and 20 of them have wasting disease. Say 100 deers are killed by hunters every year.
25 years ago, 2 of the 100 were found with wasting.
While now, 6 of the 100 are found with wasting.
Is it necessary that now out of 1000 deers, 60 have wasting disease? No.
What if the deers with wasting become slow over time? Then they would be easier to catch and hence the sample may not reflect the population.
The disease was recent at that time many years ago. Perhaps it did not yet have the impact that it does on the animal.
Now, some generations would have passed with wasting so the disease may have matured.
Also note that the other options do not weaken the conclusion at all.
(A) Wasting disease has not been discovered in domestic livestock or in moose or bighorn sheep, which are also found in significant numbers in the Rocky Mountains.
Other animals are irrelevant
(C) Since it was first reported, wasting disease has occasionally been diagnosed in deer outside the Rocky Mountains.
Outside Rocky is irrelevant.
(D) Hunters have grown more reluctant to cooperate with the authorities in reporting their deer and elk harvest, because if wasting disease is diagnosed in their harvest, the meat will be destroyed.
This just says that the sample available today from hunters may be smaller (or perhaps not if many more deer are being hunted today than they were 25 yrs ago.) No impact on our conclusion in either case.
(E) It is very difficult to diagnose wasting disease more than twenty-four hours after death, so many cases of the disease have gone undiagnosed.
Well, then it is possible that there were even more than 6% cases. It does not weaken our conclusion. If at all, it could help our conclusion.
Answer (B)