Because ethylene dibromide...

[TimL389]

Because ethylene dibromide, a chemical used to fumigate grain, was blamed for the high rate of nerve damage suffered by people who work in grain-processing plants, many such plants switched to other chemical fumigants two years ago. Since then, however, the percentage of workers at these plants who were newly diagnosed with nerve damage has not dropped significantly. Therefore, either ethylene dibromide was wrongly blamed or else the new chemicals also cause nerve damage.

Which of the following is an assumption on which the argument depends?

(A) If the new chemicals cause nerve damage, the nerve damage caused would be different from any nerve damage that ED may cause.

(B) There are no chemical fumigants that are completely safe for workers in grain-processing plants.

(C) If ED causes nerve damage, it does not take two years or longer for that damage to become detectable.

(D) Workers at grain-processing plants typically continue to work there even after being diagnosed with nerve damage.

(E) Workers at grain-processing plants that still use ED continue to have a high rate of nerve damage.

OA is C.

I'm confused with the chronology in which the events occur. If it is assumed that it does not take two years or longer for nerve damage to become detectable as a result of use of ED, then ED or the new chemicals could be the cause(s). Why does it conclude that ED was not the problem? Thanks.

[RonPurewal]

We're talking about new diagnoses of nerve damage. If we have choice C, then ethylene dibromide won't be responsible for those: it's been 2 years since ethylene dibromide was used, so, if it were at fault, the diagnoses would have been made earlier. (E.g., if it takes 1 year for ethylene dibromide to produce symptoms, then the new diagnoses would have popped up last year at the latest.)

[rakshaki]

%of new detections = no:of new cases/total no: of workers

I was tempted about option D that states the denominator remains the same.

Say there are total=100 workers.
First set of new diagnoses=10/100.
1. After eliminating the compound 20/100. and keeps increasing..Thus there is no reason to blame the compound.

I retained the 100 here as D says that the affected people have not left their jobs.

But then it now strikes me that the option merely states that the affected people have not left their jobs. It does not tell anything about the remaining workers. Thus this option should be eliminated.

Is my reasoning correct? Is this the only reason D is incorrect?

[RonPurewal]

That's still too much thinking.

We're concerned only with newly diagnosed workers.
As for what those workers do after being diagnosed—quit, keep working, retire and go fishing on the lake—we don't care.

[JbhB682]

Hi - Focusing on C

If I were to 'tweak' it

(C) If ED causes nerve damage, it does not take 2 months or longer for that damage to become detectable

Would this be a necessary assumption in that case ?

My thinking says Yes

I did select C but only because of POE

My understanding for the assumption to be a truly necessary for such conclusion is -- you should be able to detect EBD instantaneously. Any delay in detection (Even by 1 day or 1 week or 1 months) means perhaps EBD was incorrectly diagnosed as the reason behind cases prior to the switch

[Sage Pearce-Higgins]

I disagree with your thinking on this one. Note that we're told that 'many such plants switched to other chemical fumigants two years ago'. So if damage caused by ED took 2 months to present, then this damage would have already been detected. That would mean that new cases must be attributed to something else.

As with many CR problems, this one has a level of reasonable vagueness. We're told that 'the percentage of workers at these plants who were newly diagnosed with nerve damage has not dropped significantly' without being told the exact timeframe. Were sick workers diagnosed a few months ago, a few weeks ago, or perhaps even today? We're not given precise information. However, it's reasonable to assume that workers were diagnosed after ED stopped being used on multiple occasions, and that there is an ongoing problem. Of course, if we were making a scientific investigation, we'd ask for precise numbers, dates, and more details. But we're just doing a CR problem.

It's worth being clear exactly what an assumption is: an unstated premise that the argument relies on. As you wrote, something necessary for the conclusion to work. The negation test can help us find an assumption: if something is actually necessary, then removing it (i.e. making it negative) should cause the argument to fail. Let's make your supposed assumption negative: ED symptoms do not present immediately. Does the argument fail? No, because the symptoms could become detectable after, say, a week, in which case these ongoing cases of nerve damage are not due to ED, but to some other cause, and the argument survives.