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# The prevalence of a simian virus has been directly correlated with pop

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The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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Updated on: 17 May 2018, 03:10
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34% (02:21) correct 66% (02:33) wrong based on 1004 sessions

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The prevalence of a simian virus has been directly correlated with population density in gorillas. Recent fieldwork in the Republic of Dunaga, based on capturing gorillas and testing the gorillas for the virus, has shown that Morgania Plain gorillas are more than twice as likely to be infected than are the Kogula Mountain gorillas. Nevertheless, the population density of Koluga gorillas is significantly greater than that of Morgania gorillas.

Which of the following could best account for the discrepancy noted above?

A. During periods of little rainfall, Koluga gorillas often wander down into the plains in search of food.

B. Dormant strains of the simian virus are often difficult to detect.

C. Due to the Morgania gorilla’s natural habitat and its less reclusive nature, researchers have tested a greater number of Koluga gorillas than Morgania gorillas.

D. Infected Koluga gorillas behave very aggressively and are more difficult to subdue for testing.

E. The Koluga and the Morgania both have similar markings on their backs but are classified as different subspecies.

Originally posted by mba1382 on 09 Feb 2014, 20:43.
Last edited by Bunuel on 17 May 2018, 03:10, edited 2 times in total.
Renamed the topic and edited the question.
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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10 Feb 2014, 01:47
I think it's "A. During periods of little rainfall, Koluga gorillas often wander down into the plains in search of food." Coz when they wander about, their population density decreases.
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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10 Feb 2014, 02:19
anindame wrote:
I think it's "A. During periods of little rainfall, Koluga gorillas often wander down into the plains in search of food." Coz when they wander about, their population density decreases.

Can't be too sure about that can we? You are assuming that measurements is conducted during periods of rainfall, but this is not mentioned in the argument is it ?
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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10 Feb 2014, 02:33
ramannanda9 wrote:
anindame wrote:
I think it's "A. During periods of little rainfall, Koluga gorillas often wander down into the plains in search of food." Coz when they wander about, their population density decreases.

Can't be too sure about that can we? You are assuming that measurements is conducted during periods of rainfall, but this is not mentioned in the argument is it ?

Yes. I am assuming that because that seems like the best option coz if it's B then both the initial measurements and the fieldwork tests become meaningless.
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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10 Feb 2014, 02:42
anindame wrote:
ramannanda9 wrote:
anindame wrote:
I think it's "A. During periods of little rainfall, Koluga gorillas often wander down into the plains in search of food." Coz when they wander about, their population density decreases.

Can't be too sure about that can we? You are assuming that measurements is conducted during periods of rainfall, but this is not mentioned in the argument is it ?

Yes. I am assuming that because that seems like the best option coz if it's B then both the initial measurements and the fieldwork tests become meaningless.

AH but the question does not say that their density is low, it says that their density is more .
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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10 Feb 2014, 05:59
It is D. Infected gorillas are difficult to subdue for testing which implies their data is unrepresentative. ..

Posted from my mobile device
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10 Feb 2014, 06:03
Could you please elaborate more as to how the data is unrepresentative.? This will help understand your reasoning better.

abhishekjoshi wrote:
It is D. Infected gorillas are difficult to subdue for testing which implies their data is unrepresentative. ..

Posted from my mobile device
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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10 Feb 2014, 06:39
1
1
Is the reasoning this? That since Koluga gorillas are more difficult to test, no of Koluga gorillas tested is significantly lower than Morgania Plain gorillas. Therefore the no of infected cases is less for Koluga gorrillas which is why the fieldwork study found them less likely to get infected.

What is the source btw?
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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10 Feb 2014, 06:50
3
Here is the OE as below:

The greater the population density the greater the chance a gorilla is infected. Koluga gorillas have a greater population density than Morgania gorillas, therefore one would expect them to be more . Based on captured gorillas, the Morgania gorillas are more likely to be infected.

The paradox can best be resolved by (D). If scientists are far more likely to capture non-infected than infected Kogula gorillas, than that accounts for the difference in results.

(A) would be correct if the passage mentioned that researchers only captured the gorillas in the plains, and uninfected Koluga gorillas are more likely to venture out of their natural habitat.

(B)does not differentiate between the two gorillas so it unlikely to help resolve the discrepancy.

(C) is similar but different. It is not the total number of captured Kogulas that is important. ‘Twice as likely’ is based on rate not total number.

(E) is out of scope.

Source: Magoosh
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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11 Feb 2014, 00:47
1
mba1382 wrote:
Here is the OE as below:

The greater the population density the greater the chance a gorilla is infected. Koluga gorillas have a greater population density than Morgania gorillas, therefore one would expect them to be more . Based on captured gorillas, the Morgania gorillas are more likely to be infected.

The paradox can best be resolved by (D). If scientists are far more likely to capture non-infected than infected Kogula gorillas, than that accounts for the difference in results.

(A) would be correct if the passage mentioned that researchers only captured the gorillas in the plains, and uninfected Koluga gorillas are more likely to venture out of their natural habitat.

(B)does not differentiate between the two gorillas so it unlikely to help resolve the discrepancy.

(C) is similar but different. It is not the total number of captured Kogulas that is important. ‘Twice as likely’ is based on rate not total number.

(E) is out of scope.

Source: Magoosh

Yeah, but there is again an assumption here. Option D says "Infected Koluga gorillas behave very aggressively and are more difficult to subdue for testing. " It does not say that scientists are less likely to capture them, It simply is not mentioned.
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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19 Jul 2014, 15:41
Why are assuming that Gorillas need to be subdued for capturing. This is not mentioned in the question.
It is possible that Gorillas can be first trapped. In this case D cannot be the correct answer.
Also if infected Gorillas are difficult to capture, then how the research even find its numbers?

I feel A is correct. Kogulla Gorillas are denser in population and hence highly infected.
They come down the plains. Where they could have been caught for testing and reported as Morganian Plain Gorilla.

Am i missing something in my reasoning?
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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05 Feb 2015, 16:32
1
Hello,

Argument Analysis:

--- Prevalence of a simian virus is directly correlated with population density in gorillas
--- MPG more likely to be infected than KPG
--- Infection detection process in these gorillas involves capturing gorillas and testing the gorillas for the virus

Conclusion:

Nevertheless, the population density of KPG is significantly greater than that of MPG.

So, this is a paradox question.

Pre-thinking:

How to resolve this paradox? What if higher number of MPG than KPG tested for the virus? Well from this one can possibly conclude that less number of KPG were actually tested. Hence, the results that researchers are getting are biased because of the "Improper Sampling" due to their inclination to test more MPG or due to whatever other reason.

If you go through answer choices. The choice C is aligned with the above pre-thinking and hence is CREDITED response here.

Provided OA (D) dose not seems to be credited response here because:

-- Infected KPG were very difficult to subdue for testing: Well this may be true, but this does not resolve the paradox because we can not conclude that "Difficulty in testing the infected animal for virus" would have any bearing on number of animals "Actually Tested"???? May be the virus was so fatal or critical that researchers were ready to take the pain to test the "Very Aggressive KPG" also.

We don't Know.

In my opninion choice (C) appears to be correct.

Looking for expert replies on this.

Please hit kudos, if you like explanation in any way, this is great motivation to write it down.
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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Updated on: 06 Feb 2015, 02:22
Here is how I analyze the issue. 100% sure that D is the answer.

1) population density is correlated with virus prevalence
2) But the proportion of KM gorillas tested infected is lower than that of MP gorillas and KM gorillas' density is higher than MP gorillas' density.

If 1 is true then it should have been instead
"the proportion of KM gorillas tested infected is lower than that of MP gorillas and KM gorillas' density is lower than MP gorillas' density"

The discrepancy can be explained by any reasons that show that the fieldwork result is skewed or inaccurate.
(D) clearly points that the sample of KM gorillas tested is skewed due to their aggressiveness and "unwillingness to co-operate with researchers" (just kidding, this is how I make GMAT fun)

Originally posted by HoaTran on 05 Feb 2015, 20:06.
Last edited by HoaTran on 06 Feb 2015, 02:22, edited 1 time in total.
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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05 Feb 2015, 20:38
Hoa

Moreover as I wrote earlier difficulty in testing is not directly means a biased sample population in context of this argument.
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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06 Feb 2015, 07:28
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To vikasbansal227,
C is a fairly good answer, but not the best. Here is the reason:

In statistics, a small sample size makes the conclusion about the whole population less reliable.
If C is given, then the size of tested Morgania gorillas is smaller than that of tested Koluga gorillas, making the statistical conclusion (the percentage of infected gorillas) about the whole Morgania gorilla population less reliable than that about the whole Koluga gorillas population.
However, this does not explain why the infection rate of Morgania gorillas is lower or higher than that of Koluga gorillas.
There is equal chance that the smaller sample size results in lower or higher rates of infection.

Given D, "Infected Koluga gorillas ...difficult to subdue for testing". This means it is easier to capture and test the healthy Kolula gorillas. Therefore, it is likely that most of the Koluga gorillas tested are not infected, leading to a lower calculated infection rate.

I hope this clears your confusion.

Thank you for caring about my first post.^^.
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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07 Feb 2015, 03:04
I dont agree with option D.

I saw some comments, which try to explain why Koluga is twice likely to be infected.

'Koluga are unable to subdue and hence is likely to be less tested' [exactly here, i dont understand. Some comments made by people are assuming that because koluga cannot be subdued and hence less likely to be tested]

The arugumet is plainly asking the discrepancy, but is not asking what the assumptions.

need the help of a moderator. I think this question is flawed.

mba1382 wrote:
The prevalence of a simian virus has been directly correlated with population density in gorillas. Recent fieldwork in the Republic of Dunaga, based on capturing gorillas and testing the gorillas for the virus, has shown that Morgania Plain gorillas are more than twice as likely to be infected than are the Kogula Mountain gorillas. Nevertheless, the population density of Koluga gorillas is significantly greater than that of Morgania gorillas.

Which of the following could best account for the discrepancy noted above?

A. During periods of little rainfall, Koluga gorillas often wander down into the plains in search of food.
B. Dormant strains of the simian virus are often difficult to detect.
C. Due to the Morgania gorilla’s natural habitat and its less reclusive nature, researchers have tested a greater number of Koluga gorillas than Morgania gorillas.
D. Infected Koluga gorillas behave very aggressively and are more difficult to subdue for testing.
E. The Koluga and the Morgania both have similar markings on their backs but are classified as different subspecies.

Missed this one as the reasoning for OA was quite unexpected. Really good question.

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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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16 May 2015, 16:40
Lets assume that the since Infected KMG are difficult to be captured, they wont be tested since the testing requires capturing and testing. So the KMG who are not infected are tested - who are expected to have lower population density in any case - and this non-infected KMG sample results are compared with the infected MPG. So, at best, the results that say that MPG are *twice as likely* to be infected as are KMG are not true, since the # of infected KMG being captured and tested is very low and hence it follows that prob of infected KMG tested would be dispropotionately lower than the prob of capturing an infected gorilla and the prob of capturing an infected MPG gorilla (Lets assume that we have no other way of knowing whether a gorilla is infected with the virus other than the test)

Here is where I get tired of making assumptions based on leaps of faith. Option D requires us to assume that since capturing infected KMG is difficult, we wont capture those gorillas (if we assume that we wont make extra efforts to capture a randomly selected sample) and will end up capturing a lot of non infected KMG.

Since we are assuming so much in D, wouldnt it even be fair to assume some other things and validate other options?

For example, we can also assume that the Republic of Dunaga was facing drought when the tests were conducted.

mikemcgarry could you help?
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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14 Jul 2015, 19:38
Here's my approach at this question:

Available info:
1. Virus prevalence correlates with PD of gorillas. PD --> K Gorillas > M Gorillas
2. Testing Results for virus. Likelihood of disease --> M Gorillas > K Gorillas

Strategy
Look out for: Additional info, Flaw in data collection, gaps in the argument...

Options:
1. K Gorillas wandering down during rainfall could drop their PD, and hence bias our results. But no mention of rainfall being necessary to our observation: Rule Out
2. Dormant strains, OK, but do they occur differently in both types of Gorillas? Rule out
3. Could be shortlisted as lesser test subjects of M Gorillas could bias our results. But not a very convincing option. Hold this
4. Good option. If K Gorillas, who are infected, are not selected for testing, then clearly we are having a biased sample, hence flaw in data collection. Hold this, best one so far
5. Not related, not helpful in our case. Rule out

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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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14 Jul 2015, 23:48
They are difficult to test but it is not mentioned whether the scientist were able to overcome the difficulties and test them or not, whereas is option c it is clearly mentioned that the testing data was skewed.
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Re: The prevalence of a simian virus has been directly correlated with pop  [#permalink]

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29 Jul 2015, 06:16
The prevalence of a simian virus has been directly correlated with population density in gorillas. Recent fieldwork in the Republic of Dunaga, based on capturing gorillas and testing the gorillas for the virus, has shown that Morgania Plain gorillas are more than twice as likely to be infected than are the Kogula Mountain gorillas. Nevertheless, the population density of Koluga gorillas is significantly greater than that of Morgania gorillas.

Which of the following could best account for the discrepancy noted above?

A. During periods of little rainfall, Koluga gorillas often wander down into the plains in search of food.
B. Dormant strains of the simian virus are often difficult to detect.
C. Due to the Morgania gorilla’s natural habitat and its less reclusive nature, researchers have tested a greater number of Koluga gorillas than Morgania gorillas.
D. Infected Koluga gorillas behave very aggressively and are more difficult to subdue for testing.
Koluga Gorillas have not tested due to the aggressive behaviour, the data is mostly with Morgania Gorillas.. So Option D
E. The Koluga and the Morgania both have similar markings on their backs but are classified as different subspecies.

Missed this one as the reasoning for OA was quite unexpected. Really good question.

Re: The prevalence of a simian virus has been directly correlated with pop   [#permalink] 29 Jul 2015, 06:16

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