Public health official: Some researchers suspect that magnetic fields

Question

Public health official: Some researchers suspect that magnetic fields from high-voltage power lines can cause health problems for people who live especially near the lines. However, this is extremely unlikely: Beyond a distance of a few feet, the strength of the magnetic fields from high-voltage power lines is less than the average strength of magnetic fields in homes that are not located near such lines.

Which of the following would it be most useful to establish in order to evaluate the public health official's argument?

(A) Whether magnetic fields in homes that are not located near high-voltage power lines can cause health problems for the residents of those homes

(B) What proportion of people who live near high-voltage power lines believe that those lines may cause health problems

(C) Whether high-voltage power lines are routed near residential dwellings in urban areas

(D) What specific diseases or conditions are suspected by some researchers to result from exposure to magnetic fields from high-voltage power lines

(E) What is the average strength of magnetic fields in workplaces that are not located near high-voltage power lines

KarishmaB · Accepted Answer

- Magnetic fields from power lines can cause health problems to people living close by.
- Far away homes have stronger magnetic fields (caused by something else at home) than the strength of magnetic field close to power lines.

Conclusion: It is unlikely that magnetic fields from power lines cause health problems to people living close by.

Mind you, we are talking about different kinds of magnetic fields - those generated by power lines and those generated at home by other sources. We are saying that magnetic fields from power lines are weaker in people's homes that are close by. Stronger magnetic fields exist in far away homes. So it is unlikely that magnetic fields from power lines can cause health problems (because they are weaker) and stronger fields already exist.

Which of the following is useful to evaluate:

(A) Whether magnetic fields in homes that are not located near high-voltage power lines can cause health problems for the residents of those homes

We are asking whether the magnetic fields at home are harmful. If they are stronger and harmful like the magnetic fields of power lines, then it is true that weak fields of power lines may not be a source of worry. But say that magnetic fields of home at harmless - then it doesn't matter how strong they are, they will not cause any worries. The weaker fields of power lines may be a source of worry then because even the weak fields may cause health problems. 
Basically, we are trying to find out whether the two types of magnetic fields are comparable. If they are not similar, then the argument may not hold since the argument is based on this comparison.

(B) What proportion of people who live near high-voltage power lines believe that those lines may cause health problems

People's beliefs have nothing to do with what actually happens. Irrelevant.

(C) Whether high-voltage power lines are routed near residential dwellings in urban areas.

Whether residential areas are near power lines is irrelevant. We want to find out what happens when they are close to power lines.
So our argument is what happens when A happens? Whether A actually does happen or not is irrelevant.

(D) What specific diseases or conditions are suspected by some researchers to result from exposure to magnetic fields from high-voltage power lines

The actual diseases are irrelevant. We are talking about all health problems.

(E) What is the average strength of magnetic fields in workplaces that are not located near high-voltage power lines

Our argument talks only about homes, not workplaces.

Answer (A)

Marcab · Answer

Point 1: Some researchers suspect that magnetic fields from high-voltage power lines can cause health problems for people who live especially near the lines.
Point 2: Public health official states that this is very unlikely as beyond a distance of a few feet, the strength of the magnetic fields from high-voltage power lines is less than the average strength of magnetic fields in homes that are not located near such lines.

We have to evaluate whether it is unlikely that those magnetic lines have a negative effect on health of people.
 Among the available answer choices, A is relevant as it will affect the Public Official's statement most if answered affirmatively or negatively.

+1 A.
Regards,

kinjiGC · Answer

Public health official: Some researchers suspect that magnetic fields from high-voltage power lines can cause health problems for people who live especially near the lines. However, this is extremely unlikely: Beyond a distance of a few feet, the strength of the magnetic fields from high-voltage power lines is less than the average strength of magnetic fields in homes that are not located near such lines.

Which of the following would it be most useful to establish in order to evaluate the public health official's argument?

A. Whether magnetic fields in homes that are not located near high-voltage power lines can cause health problems for the residents of those homes ->  looks good , candidate of variance test to be sure.

Evaluate argument, lets take a variance test.

Lets say A) yes
Then the conclusion breaks. The conclusion is "this is extremely unlikely".
Lets say A) No.
Then the conclusion Stays.

So this is the correct answer.

B. What proportion of people who live near high-voltage power lines believe that those lines may cause health problems ->  it is not about people belief. 
C. Whether high-voltage power lines are routed near residential dwellings in urban areas ->  We are talking about areas in general.  
D. What specific diseases or conditions are suspected by some researchers to result from exposure to magnetic fields from high-voltage power lines ->  Specific disease is out of scope of the argument 
E. What is the average strength of magnetic fields in workplaces that are not located near high-voltage power lines ->  Average strength of magnetic field in the home is used for comparison, It is not required to know what is the actual value of the magnetic field. The argument deals with whether the average strength is bad enough to cause any issue.

zvazviri · Answer

Public health official: Some researchers suspect that magnetic fields from high-voltage power lines can cause health problems for people who live especially near the lines. However, this is extremely unlikely: Beyond a distance of a few feet, the strength of the magnetic fields from high-voltage power lines is less than the average strength of magnetic fields in homes that are not located near such lines.

Which of the following would it be most useful to establish in order to evaluate the public health official's argument?

A. Whether magnetic fields in homes that are not located near high-voltage power lines can cause health problems for the residents of those homes.  The premise is that the strength of magnetic field of high voltage power lines < the strength of magnetic field in homes not located close to power lines. If the magnetic field in homes is still harmful, magnetic field of high voltage might still be harmful. However, if the magnetic fields in those homes do not cause health problems, then the high voltage power lines won't cause health issues since the magnetic field is even weaker

B. What proportion of people who live near high-voltage power lines believe that those lines may cause health problems  What people believe is irrelevant; the magnetic field may not be harmful even when people believe it is

C. Whether high-voltage power lines are routed near residential dwellings in urban areas  The argument can still hold even when high-voltage power lines are routed near dwellings

D. What specific diseases or conditions are suspected by some researchers to result from exposure to magnetic fields from high-voltage power lines   Type of disease is irrelevant. We want to know whether high voltage power lines affect health. What diseases they do it doesn't matter

E. What is the average strength of magnetic fields in workplaces that are not located near high-voltage power lines  Workplaces? Argument is about homes. Out of scope

krndatta · Answer

KarishmaB  
Ma'am, 
Can you please explain option A once with the variance test and its subsequent impact on the conclusion.

KarishmaB · Answer

I only know the variance test in Stats, not in CR so I am not sure about what you are talking but I am guessing you mean the Yes/No test.

- Magnetic fields from power lines can cause health problems to people living close by.
- Far away homes have stronger magnetic fields (caused by something else at home) than the strength of magnetic field close to power lines.

Conclusion: It is unlikely that magnetic fields from power lines cause health problems to people living close by.

(A) Whether magnetic fields in homes that are not located near high-voltage power lines can cause health problems for the residents of those homes

Yes - Magnetic fields at home far from power lines can cause health problems. People in far away homes are already exposed to stronger magnetic fields but are ok. Then power line fields which are weaker than these magnetic fields are not likely to cause harm.

No - Magnetic fields at home are harmless. Then, whether they are strong or weak is irrelevant. They could be very very strong but they will still be harmless. Then how can we compare the strengths of the two types of fields and say that since power lines fields are weaker than magnetic fields at home, we don't need to worry? The weak power line fields, even though weaker than home magnetic fields, could be causing damage to people's health. We cannot give a clean chit to the power line fields by saying that they are weaker than magnetic fields already present at home. Then the reasoning of the argument doesn't work.

Hence, in the two cases, the conclusion is affected differently.

egmat · Answer

The official says: Power line magnetic fields (beyond a few feet) are  weaker  than average home magnetic fields →  therefore  power lines are unlikely to cause health problems.

The Hidden Assumption:
 This reasoning only works  if  the magnetic field level in average homes is   safe  . The official is using home field strength as a "safe benchmark."

Variance Test on Option A:
"Whether magnetic fields in homes NOT near power lines can cause health problems"

Scenario 1: YES  (home fields CAN cause health problems)
- If home-level magnetic fields are dangerous...
- And power line fields (at distance) are similar in strength...
- Then power line fields could  also be dangerous! 
- Result: Conclusion is  WEAKENED

Scenario 2: NO  (home fields CANNOT cause health problems)
- If home-level magnetic fields are safe...
- And power line fields are even weaker than home fields...
- Then power line fields are likely  safe too 
- Result: Conclusion is  STRENGTHENED

Since answering YES weakens the conclusion and NO strengthens it, Option A directly evaluates the argument.

Key Takeaway:
In Evaluate questions, the correct answer must have different impacts on the conclusion depending on whether you answer YES or NO. Option A passes this test perfectly!

minionbaba · Answer

Hi  KarishmaB ,  GMATNinja ,  MartyMurray ,  Bunuel

Can you please help me out with the below logic?

I understand why (A) is the right answer, but isn't there a deeper issue with the argument?
Suppose the magnetic field from a power line is:
 
 20 units right next to the line  
 5 units at say 25 feet away from the power line & beyond this 25 feet's distance, there are residential houses  
Now suppose an ordinary home far from any power line already has an average magnetic field of 8 units from household appliances.

The argument compares the power line's 5 units to the far-away home's 8 units and concludes the power line is unlikely to be harmful.

But wouldn't someone living near the power line (beyond the 25 feet distance) still experience the normal 8 units from their home  plus  the additional 5 units from the power line, for a total exposure of 13 units?

If so, shouldn't the relevant comparison be  13 units vs. 8 units , rather than  5 units vs. 8 units ? Even if 5 units alone is harmless, couldn't the combined exposure of 13 units still be harmful? Is this a legitimate flaw in the argument, or am I thinking about the magnetic fields incorrectly?

At option "(A) Whether magnetic fields in homes that are not located near high-voltage power lines   can cause health problems for the residents of   those   homes"

If I say YES, 8 units is bad, then the fact is home far away have 8 units, but homes near by have 13 units, so you are not comparing like-to like

Now if I say NO, 8 units is not bad, then the houses far away are safe but the houses nearby that have 13 units, are they safe or not safe? Again you are unable to compare like-to-like

KarishmaB · Answer

Sure. Whether magnetic fields have accumulative effects would be useful to know but we don't have any option that questions it.

Option (A) is questioning whether magnetic fields generated at home (say 8 units) are harmful (just as the  magnetic fields from high-voltage power lines (even if just 5 units))? The official is assuming that since it is just 5 units, it is ok. But what if it is harmful 5 units while 8 units generated at home are harmless? That is what will help us figure out whether the official's argument makes sense.

egmat · Answer

Hi minionbaba,

Your instinct is sharp, and the additive idea isn't crazy at all. But here's the catch: that  13 -unit total is something  you  are bringing to the argument — the official never said exposures stack.

Look at what the official actually compares: the strength of the power line's own field beyond a few feet (your  5 ) against the strength of an ordinary home's field (your  8 ). The whole argument is " 5  is weaker than  8 , and you already live in  8 , so  5  should be fine." Nowhere does it mention a person's  total  exposure. So when you swap in  13 , you've quietly turned it into a different argument — the classic CR slip of importing an outside mechanism the stimulus never stated.

Run option A on the argument's own terms

It's strictly  5  vs  8 , never  13 :

A = Yes  — the home's  8 -unit field is harmful → then "weaker than  8 " no longer means "safe," and a  5 -unit field could harm too.  Conclusion weakened.

A = No  — the  8 -unit field is harmless → then a field even weaker ( 5 ) is safe as well.  Conclusion strengthened.

Opposite effects → A is exactly what you'd want to establish.

A quick example to lock it in

"This new pill has a lower dose than the aspirin you already take every day, so it can't possibly hurt you."

The only thing worth establishing: is your daily aspirin actually safe for you?

Yes , aspirin's fine → "smaller than something safe" backs the claim.  Strengthens. 
 No , aspirin already upsets your stomach → "smaller than aspirin" proves nothing, since a lower dose of a  different  drug can still harm.  Weakens.

You'd never ask "but do they take the pill  on top of  the aspirin?" — the claim only set one dose against the other. Adding the doses is your move, not the argument's.

Same shape as the power-line argument: a  different  source (the pill / the power line's field) gets waved through just for being weaker than a benchmark you already live with (aspirin / your home's field) — and option A simply asks whether that benchmark is safe in the first place.

So your cumulative-effect worry is a real-world thought, just not this argument's logic — and since no answer choice is about accumulation, it can't be the thing being tested.

Public health official: Some researchers suspect that magnetic fields

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Public health official: Some researchers suspect that magnetic fields

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