Q24 - In criminal proceedings, defense attorneys

[jade.harry1]

I get this one for the most part, but could someone please explain it so I know I'm right for the right reasons? Thank you!

[ManhattanPrepLSAT1]

This is definitely a tough one. The language is very elusive.

The conclusion is that it would be a mistake to exonerate a a suspect simply because that person's DNA didn't match.

The evidence is that DNA tests often fail to distinguish among DNA samples.

Failing to distinguish among DNA samples would say that the computer has taken two samples and thought they were the same sample. That's different than taking one sample and thinking that it's two different samples.

The conclusion is about what should happen if the computer did the latter of the two. But the evidence is the former, so the evidence does not support the conclusion. Best expressed in answer choice (B).

(A) is too extreme.
(C) is not true. The argument does not generalize about the reliability of all methods.
(D) may be true, but so what? We're not talking about the difference between experimental results and nonexperimental results.
(E) is irrelevant. The argument doesn't need to show that the only form of evidence that should be permitted is physical evidence taken from the scene of the crime.

Let me know if you still need some more help with this one!

[somin.lee329]

Hi, I am still struggling with the language of the conclusion and the language in answer choice B. What is the assumption here?
Thanks!

[ericha3535]

Ok, this argument is tough so bear with me.
This argument commits the equivocation fallacy.
The conclusion and the relevant premise that supposedly supports such conclusion basically discuss two different subjects:
basically, the premise is saying: if X and Y and Z give DNA samples to the computer, the computer won't know which DNA sample comes from whom.
The conclusion however says: even if X's DNA does not match with the DNA sample from the crime scene, X should not be exonerated.

Thus, conclusion is unwarranted: since everyone's DNA is unique as said in the argument, if X's argument is different from the one from crime scene, X should be exonerated.

That's the flaw.

Now, what does B say? B is trying to point out the argument's assumption.

B is essentially saying that the argument confuses the former, which is that the DNA test that often fails to distinguish among DNA samples taken from distinct individuals, with the latter, which is that as if one person is able to give out different DNA samples.

Let me give you an example.

Paul and Jack were caught as suspects for killing a cat.
Their samples were taken in.
Paul's DNA sample was called A and Jack's sample was called B.
However, the computer said B is Paul's DNA sample where as A is Jack's sample.
Detective Johnson knew that computer would make this kind of error.
So he says "even though the DNA sample, so called C, from the crime scene does not match B nor A, Jack and Paul shouldn't be released because computer mistakes stupid mistakes all the time."
What's his assumption? He assumes each person, Paul and Jack,has this magical power to alter his DNA structure so that he might produce DNA samples that match with C.

[al2568]

Answer Choice B is written in a way that I can't grasp what it says. Anyone mind explaining it?

[ManhattanPrepLSAT1]

Answer choice (B) essentially describes the difference similar to the difference between a false negative and a false positive.

Reality: 2 samples of DNA belonging to 2 different people
Test Sees: 1 person

or

Reality: 2 samples of DNA belonging to the same person
Test Sees: 2 different people

The answer choice says the argument mistook these two different kinds of errors.

[elanaminkoff]

so I understand distinction between a false positive and false negative, but I do not see why this matters here. The DNA didnt prove to be for that person-so why does it matter which mistake is being made- shouldn't the person be exonerated because the DNA dint conclusively incriminate them?

thanks for the help!

[ohthatpatrick]

You are correct: the person SHOULD be exonerated since their DNA didn’t match the crime sample.

The author is arguing the opposite: even though the DNA didn’t match the crime sample, we should NOT let this suspect go.

Why does he think we should keep the suspect in custody? Why does the author think that the DNA test was a false negative?

Because (according to the premise), DNA tests sometimes give false positives (they fail to distinguish Bob’s DNA from Gary’s).

The author’s evidence talked about false positives: DNA tests sometimes think that Bob’s DNA is the same as Gary’s.

So his correct conclusion should be “Hence, it is a mistake to convict someone just because that person’s DNA did match the crime sample.”

His conclusion would have made sense if his evidence were about false negatives. His conclusion would have made sense if he had told us that “sometimes a DNA test fails to match a person’s DNA with that same person’s DNA from the crime scene. Hence, just because a DNA test doesn’t identify someone as a match, that doesn’t mean that the person is innocent.”

Does that clear things up?

[cacrv]

I'm definitely missing something in my understanding of B here.

I can identify the first half of B: a test that mistakenly identifies DNA samples from different people to be coming from 1 person. I can link that directly to how DNA tests often fail to distinguish among distinct samples. Done.

Where in the stim does the argument confuse this aforementioned half with a test that incorrectly concludes samples to be from different people when it was original from 1 single person?

I can see why the other four are clearly incorrect, just would love to completely understand B before moving on - thanks in advance!