Critical Reasoning

Hi Kevin,

Thankyou for your perspective on the question......But still I am not able to understand the meaning of those final lines of the argument........

May I please request you to elaborate more so as to enhance my understanding of the question.

Many thanks!

Warm Regards,
Phil

In a test, a false positive refers to a diagnosis that mistakenly indicates that a condition, disease or infection is present.
A false negative refers to a diagnosis that mistakenly indicates that a disease, infection or condition is absent.

A false positive result from a doping test could ruin the career of an honest cyclist.
A false negative result on a paternity test could prevent a father and son from reuniting


Clearly, using this test, doctors can largely avoid unnecessary removals of the appendix (eliminate false positives)without, however, performing any fewer necessary ones than before (i.e. without producing more false negatives), since .....

It seems clear that before this test was developed, doctors removed the appendix of everybody who either had appendicitis or seemed to have it (false positives).

This test has an accuracy rate of 98%, but in order for the enlarged excerpt to be true, these few mistakes must involve cases in which people without appendicitis are deemed to have it (false positives) , not the other way around. In other words, these mistakes cannot involve genuine cases of appendicitis that are classified as having nothing to do with appendicitis (false negatives), or else doctors would be performing newer necessary operations (i.e. operations on appendicitis patients) than before.

Thankyou Kevin for your analysis and perspectives.....

I am really sorry to say this that I am still not able to understand what the arg is asking for....I mean is there another shorter way to understand this question in more details.....some very basic way

also i wonder if we would have enough time in the exam to think about so many things like false positive false negative....

Please advise...

Thanks and Best Regards,
Phil

I request that you state the passage in your own words. I want to see how well you have understood it

Hi Kevin,

Based on your analysis and perspective I could understand this:


In a test, a false positive refers to a diagnosis that mistakenly indicates that a condition, disease or infection is present.
A false negative refers to a diagnosis that mistakenly indicates that a disease, infection or condition is absent.


Clearly, using this test, doctors can largely avoid unnecessary removals of the appendix (eliminate false positives)without, however, performing any fewer necessary ones than before (i.e. without producing more false negatives), since .....

I understood this line that says 'Clearly, using this test, doctors can largely avoid unnecessary removals of the appendix (eliminate false positives)' but my concern still revolves on the second line that says "without, however, performing any fewer necessary ones than before, since .....

Now when you say false negative that means disease is actually present but by mistake it is showing that it is absent....so why would they reduce false negatives...i mean they should perform more surgeries for false negative cases since the disease is actually present but by mistake it is showing that the disease is absent..........
Also the correct option for this one is B. the misdiagnoses produced by this test are always instances of attributing appendicitis to someone who does not, in fact, have it

I am somehow not able to relate the logic to the correct option B here....

It seems like may be my understanding of False negative and false positive is not perfect..

Please advise with your perspectives on my thoughts.

Best Regards,
Phil

Under what circumstances would a doctor NOT perform a necessary operation? When a patient has appendicitis but the doctor concludes (through this test, for example) that he/she does not. This would mean the that the test has produced a false negative

Just as Kevin says. If we understand the concepts of false positives and false negatives, and recognize that this question can be construed as testing those concepts, then we can solve this question quickly. But you can still solve this question without knowing about these concepts formally.

I'll try to take a shot here.

The author's conclusion is:

Clearly, using this test, doctors can largely avoid unnecessary removals of the appendix without, however, performing any fewer necessary ones than before, since .......

The part in bold basically means that, with the test, they'll still perform the same number of necessary operations (as they used to). In other words, they'll catch people who have appendicits just as much as they used to.

To complete this argument we need to find some evidence that supports the conclusion (notice the keyword "since").

How can we support the conclusion that they'll catch just as many people who have appendicits as they used to?

Well, if the 2% error rate is exclusively due to the test saying you have appendicits when you don't (rather than not catching your appendicits), then the author's argument is supported (since the error rate without the test is 20%)...that's essentially what choice B says.

As gmatmachoman points out, we can also use the denial test to prove that choce B supports the argument:

If the 2% error rate were due to the test not catching your appendicits, then the author's conclusion that the test would decrease the number of unnecessary operations is clearly weakened: the test would be decreasing the number of NECESSARY operations--clearly a bad outcome. Because the denial of choice B hurts the argument, choice B must be evidence that supports the argument.

@Eric

I think we should add this CR post in Wikiresource/Hall of fame CR posts!

Personally, I feel this CR has lots of logic being tested.I liked it very much!

@TestLuv

Thx for the explanation

IMO B is the correct answer.
Since the misdiagnoses produced by this test are always instances of attributing appendicitis to someone who does not, in fact, have it

Hence no case will be missed