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Expert witness: Ten times, and in controlled circumstances, a single d

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Expert witness: Ten times, and in controlled circumstances, a single d  [#permalink]

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New post 01 Mar 2017, 19:30
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Difficulty:

  75% (hard)

Question Stats:

54% (01:51) correct 46% (02:12) wrong based on 141 sessions

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Expert witness: Ten times, and in controlled circumstances, a single drop of the defendant's blood was allowed to fall onto the fabric. And in all ten cases, the stained area was much less than the expected 9.5 cm^2. In fact, the stained area was always between 4.5 and 4.8 cm^2. I conclude that a single drop of the defendant's blood stains much less than 9.5 cm^2 of the fabric.

Which one of the following, if true, most undermines the value of the evidence for the expert witness's conclusion?

A) If similar results had been found after 100 test drops of the defendant's blood, the evidence would be even stronger.

B) Expert witness have sometimes been known to fudge their data to accord with the prosecution's case.

C) In an eleventh test drop of the defendant's blood, the area stained was also less than 9.5 cm^2 - this time staining 9.3 cm^2.

D) Another person's blood was substituted, and in otherwise identical circumstances, stained between 9.8 and 10.6 cm^2 of the fabric.

E) Not all expert witnesses are the authorities in their fields that they claim to be.
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Re: Expert witness: Ten times, and in controlled circumstances, a single d  [#permalink]

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New post 01 Mar 2017, 20:10
the question asks us to specifically find a fact that undermines the evidence given in the stem. In such scenarios, we might see that most of the answer choices appear to weaken the conclusion, so be careful, answer to exactly what is asked.

B, E -> these statement are very generic, they don't provide any conclusions about the evidence provided in the stem, out
D -> is tempting, but again, we are asked some detail about the defendant's blood, note: this answer can be a contender but we can do better
A -> statistically, the larger the sample size the better the predictions, but again, this particular statement does not provide us with a trend towards which the set of large number of samples would lean to
C -> although not complete, but it is the best of the choices provided, it does talk about the defendant's blood sample, and also provides us with a trend, that if the expert continues to collect more samples, they would find evidence contrary to what they have concluded

C wins!
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Re: Expert witness: Ten times, and in controlled circumstances, a single d  [#permalink]

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New post 01 Mar 2017, 20:32
vikasp99 wrote:
Expert witness: Ten times, and in controlled circumstances, a single drop of the defendant's blood was allowed to fall onto the fabric. And in all ten cases, the stained area was much less than the expected 9.5 cm^2. In fact, the stained area was always between 4.5 and 4.8 cm^2. I conclude that a single drop of the defendant's blood stains much less than 9.5 cm^2 of the fabric.

Which one of the following, if true, most undermines the value of the evidence for the expert witness's conclusion?

A) If similar results had been found after 100 test drops of the defendant's blood, the evidence would be even stronger.

B) Expert witness have sometimes been known to fudge their data to accord with the prosecution's case.

C) In an eleventh test drop of the defendant's blood, the area stained was also less than 9.5 cm^2 - this time staining 9.3 cm^2.

D) Another person's blood was substituted, and in otherwise identical circumstances, stained between 9.8 and 10.6 cm^2 of the fabric.

E) Not all expert witnesses are the authorities in their fields that they claim to be.


In Assumption family questions, this is a standard format - extrapolation. The Expert analysed 10 attempts and some attempts in controlled environment(remember that these are too good to be true since the real time environment is way different from the controlled environment), and she extrapolated the data and concluded that this is a standard trend, a scenario that can be weakened if we can prove that if we try more attempts, the results can be contradictory.
Now, coming to the options,

A) If similar results had been found after 100 test drops of the defendant's blood, the evidence would be even stronger. - We do not know how good are 100 attempts. May be we need 1000 attempts to confidently extrapolate the data. We never know. The correct answer should be 100% true.

B) Expert witness have sometimes been known to fudge their data to accord with the prosecution's case. - We do not know whether the experts have fudged the data in this case. Tempting. But the options with the word sometimes have to be analysed very carefully in CR. They are usually wrong unless the conclusion is a must be true case, a scenario different from this question.

D) Another person's blood was substituted, and in otherwise identical circumstances, stained between 9.8 and 10.6 cm^2 of the fabric. - We are concerned about the defendant's blood. Irrelevant.

E) Not all expert witnesses are the authorities in their fields that they claim to be - This expert might be the authority, we do not know. Irrelevant, even if this expert is the authority. She might even fudge the data.

C) In an eleventh test drop of the defendant's blood, the area stained was also less than 9.5 cm^2 - this time staining 9.3 cm^2. - Exactly. This is in line with our analysis in the start.
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Re: Expert witness: Ten times, and in controlled circumstances, a single d  [#permalink]

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New post 01 Mar 2017, 23:50
vikasp99 wrote:
Expert witness: Ten times, and in controlled circumstances, a single drop of the defendant's blood was allowed to fall onto the fabric. And in all ten cases, the stained area was much less than the expected 9.5 cm^2. In fact, the stained area was always between 4.5 and 4.8 cm^2. I conclude that a single drop of the defendant's blood stains much less than 9.5 cm^2 of the fabric.

Which one of the following, if true, most undermines the value of the evidence for the expert witness's conclusion?

A) If similar results had been found after 100 test drops of the defendant's blood, the evidence would be even stronger. This is no strong evidence It is citing a possibility hence cannot weaken

B) Expert witness have sometimes been known to fudge their data to accord with the prosecution's case. Sometimes and a possibility cannot weaken

C) In an eleventh test drop of the defendant's blood, the area stained was also less than 9.5 cm^2 - this time staining 9.3 cm^2. This is a fact and shows that the with more trials the results are deviating . This weakens the argument.

D) Another person's blood was substituted, and in otherwise identical circumstances, stained between 9.8 and 10.6 cm^2 of the fabric. The argument is about defendant's blood not about someone else's. Tempting but Out of scope

E) Not all expert witnesses are the authorities in their fields that they claim to be. a possibility not a weakener
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Re: Expert witness: Ten times, and in controlled circumstances, a single d  [#permalink]

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New post 17 Mar 2017, 12:43
Hello expert, my query is..in option c, if with 11th drop, stained area is less than 9.5 and this is the thought process for this option to weaken the conclusion, then on similar basis, option a should also be correct because it also follows the same thought process..
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Re: Expert witness: Ten times, and in controlled circumstances, a single d  [#permalink]

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New post 17 Mar 2017, 12:52
Hey VKat, yes option A is tempting but check what it says, it tells us that 100 samples will make the evidence stronger but is that what we need? Yes, but not completely, we need a trend here, are these 100 samples trending towards covering larger area of the fabric or are they trending towards covering lesser area of the fabric. option A would be correct if it tells us this added information about the trend of these 100 samples.
Hope this is clear.

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Re: Expert witness: Ten times, and in controlled circumstances, a single d  [#permalink]

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New post 21 Mar 2017, 20:46
Please, specify the source of this question!
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Re: Expert witness: Ten times, and in controlled circumstances, a single d &nbs [#permalink] 21 Mar 2017, 20:46
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Expert witness: Ten times, and in controlled circumstances, a single d

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