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# The prevalence of a simian virus has been directly correlate

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Re: The prevalence of a simian virus has been directly correlate [#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 correlate [#permalink]

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06 Feb 2015, 07:28
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 correlate [#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 correlate [#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 correlate [#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 correlate [#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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The prevalence of a simian virus has been directly correlate [#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.

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Re: The prevalence of a simian virus has been directly correlate [#permalink]

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21 Dec 2015, 03:53
Hi mikemcgarry

basically in this question we are testing two kind of gorillas to know they are infected from virus or not.

in other words its an sampling question. we are taking samples and then concluding .

here in option C and D both indicates sampling is not proper then why D is better then C?

according to option C if we take 100 gorillas of type M and 10 gorillas of type K then also sampling is biased.

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Re: The prevalence of a simian virus has been directly correlate [#permalink]

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21 Dec 2015, 20:44
When i read the question it sounds like there is no paradox at all. MPG is more likely to be infected than KPG. So odds against the number of MPG is more than KPG. So is the survey. Population density of KPG > population density of MPG. Had the survey been the other way then there is a paradox. I would like to know what others think. Paradox should have conflicting ideas and here both are linear.

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Re: The prevalence of a simian virus has been directly correlate [#permalink]

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06 Feb 2016, 12:05
I went with C, since the results of the tests are biased.Note that the likelihood of the infection is pure speculation, as the evidence is based on the results of the tests.
Suppose we tested 100 MG and 10 KG.
from tested MG, 10 are infected
from tested 10 KG, 5 are infected.
But what if from the whole population of KG, the infected ones are much more? say 50%?

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The prevalence of a simian virus has been directly correlate [#permalink]

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07 Feb 2016, 08:07
pkm9995109794 wrote:
When i read the question it sounds like there is no paradox at all. MPG is more likely to be infected than KPG. So odds against the number of MPG is more than KPG. So is the survey. Population density of KPG > population density of MPG. Had the survey been the other way then there is a paradox. I would like to know what others think. Paradox should have conflicting ideas and here both are linear.

I think there is a paradox. It is really subtle
By 'More likely' they mean more than 50% .Lets say 70%. So 70% OF POPULATION OF MPG is infected AND MPG Population is less dense ..... (1)
Now that MPG is twice more likely than KPG , that means only 35% OF POPULATION OF KPG is infected AND KPG Population is highly dense .... (2)
FROM (1) & (2) => More Dense population has LESS Prevelence (LESS % of infected) ....... (3)
BUT
What The First line says ? Prevalence is directly proportional to density .
So THE MORE DENSE the population , THE MORE % of Infected
Is this we get from (3)? No just the opposite

D resolves it
D says ,
may be , because of aggressiveness of infected KPG they are less tested. And hence the resulting DATA is merely an approximation and hence does not reflect the practical Number
And
may be , because of calmness of infected MPG , they are well tested and hence the DATA is more accurate
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Re: The prevalence of a simian virus has been directly correlate [#permalink]

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08 Feb 2016, 18:40
tryambaks You are correct.

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Re: The prevalence of a simian virus has been directly correlate [#permalink]

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19 Dec 2017, 17:53
Nice Question

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Re: The prevalence of a simian virus has been directly correlate [#permalink]

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19 Dec 2017, 17:57
Premise: Simian virus is directly correlated with the population density in gorillas. That is, More the population density(no. of gorillas in a square kilometre or mile) more the simian virus. In layman terms , the more crowded the area the more is simian virus. SIMIAN VIRUS IS CONTAGIOUS. (This has to be kept in mind and is not given explicitly in the stimulus).
Premise: Republic of Dunaga has 2 areas Morgania Plain and Kogula Mountains. There are gorillas in these 2 areas... both are classified differently respective to their habitats.

Conclusion 1: Morgania Plain gorillas are more infected than Koluga gorillas.
Conclusion 2: The popualation density of Koluga gorillas is greater than Morgania gorillas.
What does that mean Koluga gorillas should me infected more than Morgania gorillas. But,we have a discrepancy in the results.

A: Kolugans leave mountains and wander in plains of Morgania for food... so the researchers might have mistaken the identity of Kolugans... this isnt possible once one does classification of gorillas. After classification researchers will not miss the identity. Wrong Answer.

B: Dormant strains of virus are often difficult to detect... so this assumes that Kolugans might have dormant strains of virus... which were not found in the testing. Could be the answer.. lets keep this.

C: More Kolugans and less Morganians... should yield more Kolugan virus infected gorillas and less Morganian virus infected gorillas.. since Kolugans have greater population density ... that is they live a lot closer to each other.. the greater the virus too.. from the stimulus. This choice contradicts the stimulus ... Wrong Answer.

D: Kolugans once infected anre more difficult to testing... could be the answer as... since these gorillas behaved agressively once infected...and hence were difficult to test.. there was lesser data available for Kolugans.. with respect to Morganians. Keep this one..

E:Both have similar markings but different subspecies... its fine... but classification takes into account many things and does not depend only on visual identity. So this is wrong.

Analysing our winners we have B and D.

B:Dormant strains are difficult to test... but can be tested with advanced techniques.
D: Aggressive gorillas are difficult to test... but can be tested if subdued.. which is again difficult to test.

Lets see the meaning of dormant.. it says something which is inactive.. here we have inactive virus.. and can be activated once the conditions are right.. that is still the gorillas are infected. Dormant or not dormant the virus is still present.

So finally we arrive at D. The answer.

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The prevalence of a simian virus has been directly correlate [#permalink]

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15 Jan 2018, 05:22
C makes the problem worse. It is because C should only explains the test results, but cannot explain why population density of Koluga gorillas is greater.
Hence, C is a great trap.
There is a similar question in which the answer is still D, but the trap is that regularly travels to other area.

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Re: The prevalence of a simian virus has been directly correlate [#permalink]

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16 Jan 2018, 02:13
why option d is correct instead of option c

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Re: The prevalence of a simian virus has been directly correlate [#permalink]

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16 Jan 2018, 17:47
rishabhmishra wrote:
why option d is correct instead of option c

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

IMO, you are confusing numbers with percent values.

Option C says - More Koluga were tested than Morgania. So we have more sample for Koluga but it doesn't explain the discrepancy in finding. We need some reason in sample size for the discrepancy. Now option D, It is hard to catch infected Koluga so the team is more successful in catching uninfected Koluga thus making our tested population bias.
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Re: The prevalence of a simian virus has been directly correlate   [#permalink] 16 Jan 2018, 17:47

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