Smoking is a known cause of certain serious health problems, including

Question

Smoking is a known cause of certain serious health problems, including emphysema and lung cancer. Now, an additional concern can be added to the list of maladies caused by smoking. A recent study surveyed both smokers and nonsmokers, and found that smokers are significantly more anxious and nervous than nonsmokers.

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

(A) Anxiety and nervousness can lead to serious health problems.

(B) Anxiety and nervousness do not make individuals more likely to start smoking.

(C) Equivalent numbers of smokers and nonsmokers were surveyed for the study.

(D) Smokers are aware of the various health problems attributed to smoking, including lung cancer and emphysema.

(E) Smokers who had smoked a cigarette immediately before responding to the survey were more anxious and nervous than smokers who had not smoked for several hours.

pqhai · Accepted Answer

This is a classical “ cause and effect ” question.
 The form is: 
 Both A and B exist
Conclusion: A causes B happen.
Assumption: B does not cause A  (the reverse relationship is not correct)

ANALYZE THE STIMULUS:

Fact: smokers have more anxious and nervous than nonsmokers
Conclusion: smoking leads to more anxious and nervous  (note: the conclusion is inferred )
 Assumption:  Anxiety and nervousness do not lead to smoking

ANALYZE EACH ANSWER:

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

a) Anxiety and nervousness can lead to serious health problems. 
 Wrong.  
The flow is: 
X - smoking ==> Z -serious health problems. 
--AND—
Y - anxiety and nervousness ==> Z- serious health problems. 
Clearly, it does not mean X must lead to Y just because both X and Y lead to Z. It’s totally wrong logic.

b) Anxiety and nervousness do not make individuals more likely to start smoking. 
  Correct.   This is cause & effect question. Smoking leads to anxiety and nervousness only if Anxiety and nervousness do not make people smoke.

c) Equivalent numbers of smokers and nonsmokers were surveyed for the study. 
 Wrong.  C is  TEMPTING  but wrong. Assume you have a whole population 1 million people. You're supposed to take survey, you need 1000 non-smokers and 1000 smokers in order to have a good sample. 
==> Clearly, your  sample is perfect  to have a reliable conclusion if you have  exactly  1000 non-smokers and 1000 smokers.

What if you take 1100 non-smokers and 1000 smokers ( in-equivalent numbers ), your conclusion will not be reliable? Nope, because  1000 is a base  in order to get conclusion reliable. If you  add  2 or 3 people in the sample, your conclusion is still reliable. 
Thus, C is not an assumption. (because if you negate the assumption, the conclusion MUST be incorrect).
 Note:  the stimulus talk about "the survey" which implies "sampling technique".

d) Smokers are aware of the various health problems attributed to smoking, including lung cancer and emphysema. 
 Wrong.  The fact people are aware of health problems attributed to smoking does not mean smoking leading to anxiety and nervousness.

e) Smokers who had smoked a cigarette immediately before responding to the survey were more anxious and nervous than smokers who had not smoked for several hours.
 Wrong.  Clearly out of scope. We talk about smokers in general, NOT only smokers who had smoked a cigarette immediately before responding to the survey.

Hope it helps.

Bunuel · Answer

OFFICIAL EXPLANATION

Although the premises of this argument suggest only a correlation between smoking and anxiety or nervousness, the argument has a causal conclusion: it concludes that smoking causes individuals to be anxious and nervous (i.e., that A causes B). Any assumption in a causal argument must support the causal “direction” of the conclusion, that A causes B as opposed to some other explanation. Often, assumptions support a causal conclusion either by eliminating an alternate cause for the conclusion (that C did not cause B) or by demonstrating that the causation, if one exists, is in the proper direction (that B did not cause A).

(A) The argument concludes that smoking causes anxiety and nervousness. Whether these maladies lead to more serious health problems is not relevant to the conclusion.

(B) CORRECT.  For smoking to be the cause of anxiety and nervousness (i.e., that A caused B) it must be true that these individuals were not more likely to be anxious and nervous before they started smoking. If smokers had these preconditions, which contributed to their decision to begin smoking (i.e., that B caused A), our conclusion – that smoking causes these maladies – would be incorrect.

(C) The argument concludes that smoking causes anxiety and nervousness. The number of survey respondents is not relevant to the conclusion.

(D) The argument concludes that smoking causes anxiety and nervousness. The awareness of the health problems related to smoking is not relevant to the conclusion.

(E) The argument is not based on the immediate impact that smoking has on anxiety and nervousness. Moreover, the argument never compares some smokers to other smokers.

jaituteja · Answer

Hi pqhai,

The argument states that "A recent study surveyed both smokers and nonsmokers". So we have to assume that the no. of people taking survey were equal.
Suppose i survey, 1000 Smokers and 100 Non-smokers, my conclusion holds true, but is invalid because the base of comparison is not same.

Can you explain why option C is incorrect??

Thanks,
Jai

pqhai · Answer

Hi Jai

The base of comparison is not the same does not mean the comparison invalid  in statistics.  I'm really sorry but I assume you have some ideas of statistics. So I will explain by using statistic example.

For example: You have a whole population 1 million people (including both non-smokers and smokers). To get 99% reliable conclusion, you MUST have a sample which includes 100 non-smokers and 100 smokers (perfect sample). There are two scenarios:

(1) you have a sample including fewer than 100 non-smokers and 100 smokers, your conclusion is NOT reliable. Because your sample is not standard.
(2) you have a sample including 101 non-smoker and 100 smokers, however, your conclusion is NOT more reliable.

The ONLY 100% correct in statistic is when you ask all 1 million people. If you take a survey, you're doing statistic. Thus we just talk about "reliable" term, not "absolute" /100% correct. Standard deviation must exist.

C says the number of non-smokers and that of smoker must be equal. However, by using example above we can show that even when the numbers are not equal, the conclusion still holds true.

Hope it helps.

BillyZ · Answer

Assumptions and Causality

“When a GMAT speaker concludes that one occurrence caused another, that speaker also assumes that  the stated cause is the only possible cause  of the effect and that  the stated cause will always produce the effect .”

Thus, because the author always assumes that  the stated cause is the only cause , Assumption answer choices tend to work exactly like Strengthen answer choices in arguments with causal reasoning. The correct answer to an Assumption question will normally fit one of the following categories:

A. Eliminates an alternate cause for the stated effect

Because the author believes there is only one cause (the stated cause in the argument), the author assumes no other cause exists.

B. Shows that when the cause occurs, the effect occurs

Because the author believes that the cause always produces the effect, assumption answers will affirm this relationship.

C. Shows that when the cause does not occur, the effect does not occur

Using the reasoning in the previous point, the author will always assume that when the cause does not occur, the effect will not occur.

D. Eliminates the possibility that the stated relationship is reversed

Because the author believes that the cause-and-effect relationship is correctly stated, the author assumes that the relationship cannot be backwards (the claimed effect is actually the cause of the claimed cause).

E. Shows that the data used to make the causal statement are accurate, or eliminates possible problems with the data

If the data used to make a causal statement are in error, then the validity of the causal claim is in question. The author assumes that this cannot be the case and that the data are accurate.

The above categories should be easy to identify because you should have already memorized them from the Strengthen question section. From now on, when you encounter Assumption questions containing causal reasoning, you will be amazed at how obvious the correct answer will seem. These types of patterns within questions are what make improvement on the GMAT possible, and when you become comfortable with the ideas, your speed will also increase.

jabhatta2 · Answer

Hi  avigutman  : I understand in causal arguments   .... it hurts the causal nature of the argument, if B --> A.

At this point i have memorized it (i dont think I have internalized it)

In order to internalize, here is my attempt. I was wondering if I my thinking is accurate in my second post below for this arguement i made up

Conclusion : Research of 100 people shows that    Depression (A) leads to Obesity (B)   .

This implies the following chain of commands.

Individual starts of non-obese AND non - depressed --> first gets depression only --> then becomes obese only AFTER the depression

jabhatta2 · Answer

If the opposite is also true that Obesity (B) --> Depression (A), then this hurts the original argument (A --> B) because

Most likely, out of the 100 people surveyed, one surveyed person MAY (not gauranteed) have been Obese first and then became Depressed. Thus for this one individual, the chain of events is actually

B (Obese first) --> A (Depression second) --> Given he is obese and depressed at the same time, we dont know if this person will get EVEN  MORE  obese than his initial obesity level.    
OR 
  B (Obese first) --> A (Depression second) --> Given he is depressed and obese at the same time we dont know if he will continue to maintain his initial obesity level

Gievn we don't know which of the two chain of sequences will happen for this individual, we can't say A --> B

Am i thinking about this right or completely off base ?

avigutman · Answer

That's not bad,  jabhatta2 . You're just missing the premise that led to your conclusion, something like "research has shown that obese people tend to be depressed".

Here's how I think about this type of argument:

We know the GMAT loves arguments that put forth as a conclusion one particular explanation for some surprising phenomenon.
What we're dealing with here is a subset of those. In this case, the surprising phenomenon is a correlation between A and B, and one possible explanation for that phenomenon is that A causes B. An alternative explanation could be that B causes A, and that would weaken the conclusion (an alternative explanation always weakens a conclusion that puts forth one particular explanation for a phenomenon).

Another example: every morning when I wake up and open my eyes I see that the sun is rising (surprising phenomenon, A and B are correlated).
Therefore, my awakening must be causing the sun to rise (one possible explanation for the phenomenon).

Weakener: I don't have blinds on my windows. This suggests that perhaps it's not my awakening that causes the sun to rise, but rather the rising sun is causing me to wake up.

jabhatta2 · Answer

Thanks so much  avigutman . Here is another one, which helps me internalize what you said above.

Surprising phenomena  : Tom and Samantha are always seen together. 
 Reason given by GMAT  - Tom must be stalking Samantha

Weakener  : Actually Samantha is stalking Tom

If Samantha is instead stalking Tom -- that why Tom and Samantha are seen together AND this weakens the reason given my GMAT specifically.

That is why B --> A is always a weakener. It provides ANOTHER explanation for the surprising phenomena

Thank you !

Its much easier to understand now

VerbalBot · Answer

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