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

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!

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.

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

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..

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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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.

Premise: 10 tests show a drop stains 4.5 - 4.8 cm^2
Conclusion: a single drop of 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. No info on how much test is required. So if 3 suffice the court requirement for a reliable evidence, doing 10 is good enough. Doing 100 is just waste of time

B) Expert witness have sometimes been known to fudge their data to accord with the prosecution's case. This attack the expert witness's past. This should not be considered in the current 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. Yes. It attacks the part "much less". As in one circumstance, the result is very near the 9.5 cm^2 limit, it is unreasonable to conclude confidently that a single drop stains an area much smaller than 9.5 cm^2. It may be well that all the first 10 tests are wrong

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 claim is about the defendant's blood. Another person's blood is not of interest

E) Not all expert witnesses are the authorities in their fields that they claim to be. So what? This is so general, it doesn't attack the conclusion or the gap or any info in the argument

D strengthens the argument and is not at all tempting. From D we can conclude that the size of the stain DO vary between people, and that there is a reason to have faith in the evidence presented.

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Keep an eye for modifiers in the conclusion of an argument in CR question.



Straight C.
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Hi expert,
Could you help on D? I know some people said it is irrelevant of another person’s blood, but I think this explanation is weird. The conclusion discusses about blood drop stains, is there any difference of blood drop between ordinary people and defendants, all people are human beings?
Looking forward to your kindly opinion, and much thanks.

Yes, the idea is that people's blood is not all the same. So, the fact that the sizes of the stains created by a different person's blood are different does not undermine the support for the prediction provided by the sizes of the stains created by the defendant's blood.
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D is somewhat a strengthener(not strongly though) as defendant's blood still stains much less than 9.5 cm^2 of the fabric. However, it is irrelevant at best.
E is generic statement that does nothing to the passage.
B, similar to E, is generic in nature. Has this expert witness fudged anything. We don't know, neither knowing so would help.
A is testing the sampling aspect which becomes irrelevant if stained area is not known.
C is relatively good among the available choices, however, not the best as we would have liked.

Answer C.
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