blog wrote:
A chemical company claims that, since only one of 520 rats that were given high doses of a new artificial sweetener developed cancer while all the others remained healthy, the sweetener is not carcinogenic for human beings and ought to be approved for
human consumption.
Which of the following, if true, most strongly supports the chemical company’s claim?
(A) Chemicals that are carcinogenic for rats are usually also carcinogenic for other animals, such as guinea pigs, used in experiments.
(B) The spontaneous incidence of cancer in this particular strain of rat is approximately one in 540.
(C) Tests conducted on a certain strain of mouse show that, of 500 mice given a dose of sweetener similar to that given the rats, 53 developed cancer.
(D) Certain chemicals that are carcinogenic for human beings have been shown not to be carcinogenic for rats.
(E) The average lifespan of the strain of rat used in the experiment is 2 years the chemical company terminated the experiment when the rats were 13 months old.
mSKR - Ian has already explained why (B) works so nothing left for me to add on that.
I am giving my analysis of the other options below.
Company's Claim: The sweetener was given to 520 rats and only 1 got cancer.
Company's Conclusion: The sweetener is not carcinogenic for human beings and ought to be approved for
human consumption.
There are multiple things I need to know before I can say whether the company's claim is valid:
1. Do rats normally get cancer? If no, then why did that 1 rat get it? Perhaps the sweetener is carcinogenic then. If yes, what is the normal rate of occurrence in rats? If 1 in 10,000 rats get cancer then the sweetener may have had a bad effect. If 1 in 20 rats get cancer then the sweetener may actually be acting as anti-cancer! If 1 in 500 rats gets cancer then it seems the sweetener has no link to cancer.
2. Do human beings also experience the same effect of chemicals as do rats? If yes, then it seems the company's conclusion is justified. If no, then perhaps the company's conclusion is not justified.
We need something that supports the company's claim i.e. something that says that the sweetener is not carcinogenic.
(A) Chemicals that are carcinogenic for rats are usually also carcinogenic for other animals, such as guinea pigs, used in experiments.
This tells us that other animals used in experiments also experience effects similar to rats. But what about humans? How similar or different their reactions are? The similarity between all animals that are experimented on is irrelevant to us. We need to know the differences/similarity between those animals and humans.
(B) The spontaneous incidence of cancer in this particular strain of rat is approximately one in 540.
Correct. As discussed above, we were looking for this information. If naturally 1 in 540 rats gets cancer then it looks like the sweetener is not linked to cancer.
(C) Tests conducted on a certain strain of mouse show that, of 500 mice given a dose of sweetener similar to that given the rats, 53 developed cancer.
Are mice similar to humans? If they are, then this weakens our conclusion.
(D) Certain chemicals that are carcinogenic for human beings have been shown not to be carcinogenic for rats.
So this says that rats and humans are not very similar. Some chemicals could be carcinogenic in humans even if they are not in rats. Then this weakens the company's conclusion.
(E) The average lifespan of the strain of rat used in the experiment is 2 years the chemical company terminated the experiment when the rats were 13 months old.
This again puts a question mark on the company's conclusion. The rats could have developed cancer later. Hence, it doesn't strengthen the conclusion.
Answer (B)