Epidemiologist: A study of residents in 116 of our nation's cities

Epidemiologist: A study of residents in 116 of our nation's cities found that, on average, the incidence of cardiovascular disease was significantly higher in residents of the cities whose air was more polluted with soot particles. This shows that reducing soot pollution in those cities would lower the risk of cardiovascular disease for the residents.

The conclusion of the argument is the following:

reducing soot pollution in those cities would lower the risk of cardiovascular disease for the residents

The support for the conclusion is the following premise:

A study of residents in 116 of our nation's cities found that, on average, the incidence of cardiovascular disease was significantly higher in residents of the cities whose air was more polluted with soot particles.

We see that the epidemiologist's reasoning is basically that there is some kind of causal connection between pollution of air with soot particles and the incidence of cardiovascular disease in a city.

The question asks which of the choices would most weaken the argument. So, the correct answer will show that, even though the premise is true, the epidemiologist's conclusion may not be correct.

A. A high proportion of residents in the cities whose air is more heavily polluted with soot particles have lifestyles that lower the risk of cardiovascular disease.

This choice strengthens the argument.

After all, if what this choice says is true, then we know that the lifestyles of the people in the cities in question are not causing them to experience cardiovascular disease. In fact, their lifestyles would be expected to reduce the risk of cardiovascular disease.

So, this choice serves to eliminate the possibility that people's lifestyles are causing the higher incidences of cardiovascular disease, making it more likely that the soot pollution is causing it.

A choice that strengthens the argument will never be the correct answer to a Weaken question.

Eliminate.

B. The study failed to measure the incidence of cardiovascular disease in rural areas where there is little or no soot pollution.

This choice tempts us to choose it as a weakener by seeming to suggest that the methodology of the study was lacking a key element.

So, what we need to notice is that, since the study involves a comparison of what goes on in cities with more and less soot pollution, it does not need to also measure the incidence of cardiovascular disease in rural areas. It has already provided reason to believe that soot pollution causes cardiovascular disease.

In fact, by including statistics from rural areas, the study might become less valid since any pattern seen in rural areas could be the result of the fact that they are rural rather than of the levels of soot pollution in those areas.

Eliminate.

C. On average, among the 116 cities, the residents of cities whose air has less soot pollution have diets much less likely to cause cardiovascular disease.

This choice weakens the argument.

After all, if what this choice says is true, then it could be that the reason the incidences of cardiovascular disease are lower in the cities with less soot pollution is that people in those cities have diets much less likely to cause cardiovascular disease.

In that case, the evidence that the incidence of cardiovascular disease was significantly higher in residents of the cities whose air was more polluted with soot particles does not effectively support the conclusion. After all, even though that premise is true, we have reason to doubt that the conclusion is correct since there's another variable, diet, that could be the true cause of the difference in incidences of cardiovascular disease.

Keep.

D. After soot pollution in one city was dramatically reduced, the incidence of cardiovascular disease in that city remained above the national average.

This choice does seem to weaken the argument because it seems to indicate that, even without soot pollution, the risk of cardiovascular disease remained high.

Notice, however, that the fact that the incidence of cardiovascular disease in one city remained "above the national average" does not tell us much. After al, the national average includes EVERYONE that lives in the country, including people who do not live in cities at all.

So, the implications of the information provided by this choice are not clear. After all, it could be that the incidence of cardiovascular disease in ALL cities is higher than average in a nation in which people may also live in rural and suburban areas.

Also, the fact that this outcome occurred in one city does not really change what we know since the evidence in support of the conclusion is that "ON AVERAGE, the incidence of cardiovascular disease was significantly higher in residents of the cities whose air was more polluted with soot particles." So, even though this one city does not fit the overall pattern, that overall pattern that supports the conclusion still exists.

Eliminate.

E. Reducing soot pollution would also involve reducing several other forms of air pollution that contribute more significantly to cardiovascular disease.

The conclusion is that "reducing soot pollution in those cities would lower the risk of cardiovascular disease for the residents."

So, if what this choice says is true, then we have even more reason to believe the conclusion since the recommended action, "reducing soot pollution," would likely reduce the presence of multiple causes of cardiovascular disease in addition to soot pollution.

So, this choice strengthens, rather than weakens, the case for the conclusion.

Eliminate.

The correct answer is (C).

Epidemiologist: A study of residents in 116 of our nation's cities found that, on average, the incidence of cardiovascular disease was significantly higher in residents of the cities whose air was more polluted with soot particles. This shows that reducing soot pollution in those cities would lower the risk of cardiovascular disease for the residents.

Which of the following, if true, would most weaken the epidemiologist's argument?

A. A high proportion of residents in the cities whose air is more heavily polluted with soot particles have lifestyles that lower the risk of cardiovascular disease.

B. The study failed to measure the incidence of cardiovascular disease in rural areas where there is little or no soot pollution.

C. On average, among the 116 cities, the residents of cities whose air has less soot pollution have diets much less likely to cause cardiovascular disease.

D. After soot pollution in one city was dramatically reduced, the incidence of cardiovascular disease in that city remained above the national average.

E. Reducing soot pollution would also involve reducing several other forms of air pollution that contribute more significantly to cardiovascular disease.

The passage says that cities with a lot of soot in the air have residents that are worse off when it comes to cardiovascular disease. That it would therefore be good to reduce soot to reduce this disease.

We're asked to find something that weakens this.

(C) is the answer. If cities with less soot have residents that have a diet MUCH LESS likely to cause cardiovascular disease, you have an ALTERNATE explanation for why those residents are less likely to have the disease. Basically, it reduces the link between soot causing the disease.

-contact: gmatknight site | gmatclub dm

OA: C; this option captures the essence of the original sentences, and does the most to weaken it.

Understanding the argument - 
­Epidemiologist: A study of residents in 116 of our nation's cities found that, on average, the incidence of cardiovascular disease was significantly higher in residents of the cities whose air was more polluted with soot particles. - Fact. 
This shows that reducing soot pollution in those cities would lower the risk of cardiovascular disease for the residents. - Conclusion. It establishes the causal connection between "soot particles" and "risk of cardiovascular disease." 

Which of the following, if true, would most weaken the epidemiologist's argument?

Option Elimination: We need to break or weaken the causal connection. Remember, we don't need to bury the argument; we need something that can move the needle - even if it is small or creates doubt. 

A. A high proportion of residents in the cities whose air is more heavily polluted with soot particles have lifestyles that lower the risk of cardiovascular disease. - So, those lifestyles should ideally reduce the risk of cardiovascular disease, but they don't help. Why? It may be because of soot particles. This option removes the possible objection and further strengthens the conclusion. Opposite of what we need.  

B. The study failed to measure the incidence of cardiovascular disease in rural areas where there is little or no soot pollution. - The scope of our argument is "116 of our nation's cities." Out of scope. 

C. On average, among the 116 cities, the residents of cities whose air has less soot pollution have diets much less likely to cause cardiovascular disease. - so the soot pollution is less, and their diet is less likely to cause cardiovascular disease. So, diets may be responsible for lowering cardiovascular disease. It can very well be because of lower soot pollution, but this option now casts doubt on it, which is what we need as a weakened. Remember, we are not looking for a Thor's hammer to shatter the argument and bury it in the ground. We are just looking for an option that moves the needle, however small. Ok. 

D. After soot pollution in one city was dramatically reduced, the incidence of cardiovascular disease in that city remained above the national average. - one city doesn't affect the conclusion, which is still valid. Distortion. 

E. Reducing soot pollution would also involve reducing several other forms of air pollution that contribute more significantly to cardiovascular disease. - strengthener­