pretest 33, section 1 #17

[mchuynh]

I eliminated D because I thought it was out of scoped. "Another person's blood" isn't relevant.

I didn't pick C because i thought it wouldn't really weaken the argument. The author might have second thoughts, but the argument doesn't necessarily fall apart though?

Can someone explain to me why C is the right answer? Thanks

[aileenann]

Sometimes when you are trying to weaken, you won't find an answer choice that makes the argument fall apart entirely. Sometimes you will only do a mediocre level of damage, but it's the best available option.

Here, (C) is your best option. What it gets at is two things. First, the test seems to be unreliable if it could give such widely variable results (4 to 9 is a big difference). Second, it suggests that if the 11th result is the best one (and we don't have a way of knowing which one is the best one), this suggests it could very well be the defendant's blood. You might still point to the other 10 test results, but as it stands we still have one data point that should concern us.

Can you explain why the wrong answer choices are not as good a weakener as (C)?

[todavidzheng]

Could anyone explain why B is wrong?

[bbirdwell]

Mostly, (B) is wrong because (C) is way better.

We are trying to weaken the value of the evidence in reaching the conclusion that D's blood stains an area MUCH LESS than 9.5cm.

Demonstrating that one drop of D's blood stained 9.3cm directly weakens that connection.

The key in tough weaken questions is to focus on the CONNECTION between the evidence presented and the conclusion.

(A) may be true, but that doesn't make this example weak.

(B) sort of goes after the premise itself (and that not very well), which is sort of a logical faux pas. The fact that some witnesses fudge their data doesn't say anything at all about THIS witness.
This would be a better weakener if the argument said something more like "the defendant is guilty, because the expert witness said so."

(D) out of scope -- another's blood

(E) is out for the same reason as (B). So what? That doesn't tell us anything about THIS witness.