Appendicitis (inflammation of the appendix) is potentially fatal; cons

B for meIf you overdiagnose cases, you will end up doing more than required surgeries but you will not miss any necessary ones. This is a case of false-positives. False-positives are always better than false-negatives. This way you will not miss any true-positive cases.

Should be (B)

Say 80 out of 100 cases were correctly diagnosed per the previous surgery. Using the new scan, how would you ensure that the 80 surgeries that were previously diagnosed correctly will continue to be accurately detected? This is possible only when the new scan detects 98 surgeries that are correct (AND INCLUDES the 80 correct ones from the earlier surgery) and perhaps misdiagnoses 2 (that are essentially false positives). It is essential that these 2 be false positives, as the new scan should not leave out any real cases that were correctly identified before.

B.

The answer seems obvious when you rephrase the last sentence of the question as: new tech lowers instances of false positive but does not lower those of real positive since____

Answer: the misdiagnosis is always false positive instead of false negative.

Basically the info that fills the blank is the one that suggests why in spite of using the internal scan the number of surgery performed will not decrease. We need some information regarding the misdiagnosed case. B fills the gap saying the misdiagnosed cases are infact not the misdiagnosed ones; they actually dont have appendicitis. hence the number actually infected is not reduced and hence the necessary removals will not decrease.

Hence B.

Hope this helps..!!

It is a really tough question.

I initially picked C but after reading other people's opinions, realized that the correct answer must be B.
My understanding is like this. Feel free to point out any flaws.

Before a newly developed internal scan, the surgery was performed unneccessarily in about 20 percent.
(We can say from this statement that of the patients who underwent this surgery, 20 percents didn't actually have Appendictis. I can assume that those unneccessary surgery were caused by misdiagnoses.)

The newly developed internal scan lowered the chance of misdiagnoses.

This newly developed internal scan enables doctors to avoid unnecessary surgery but doesn't lower the number od incidents that patients who need the surgery don't get the surgery.

As people say, misdisgnoses have two cases. 1. actually have one but diagnoed as not having
2. actually don't have one but diagnosed as having.

In the case 1, patients need the surgery but don't get it.
In the case 2, patients don't need the surgery but get it.

If misdiagnoses with the newly developed internal scan is only case 2, unneccessary surgery can be reduced because the number of misdiagonoses is decreased while neccessary sugery is not decreased.

Just to be sure - The OA is B) and the question is part of GMATPrep Exam Pack 1 - Mock 3

Appendicitis (inflammation of the appendix) is potentially fatal; consequently, patients with symptoms strongly suggesting appendicitis almost have their appendix removed. The appropriate surgery is low-risk but performed unnecessarily in about 20 percent of all cases. A newly developed internal scan for appendicitis is highly accurate, producing two misdiagnoses for every 98 correct diagnoses. Clearly, using this test, doctors can largely avoid unnecessary removals of the appendix without, however, performing any fewer necessary ones than before, since _____ .

Basically, the doctors can reduce the unnecessary operations but cannot avoid the necessary operations, using the new test. So, misdiagnosis is always shows Positive for negative cases or false negative cases. If it is the other way around, the false positive cases, the doctors will be performing more necessary removals.

A. the patients who are correctly diagnosed with this test as not having appendicitis invariably have medical conditions that are much less serious than appendicitis
- OFS as we are not talking about other medical conditions

B. the misdiagnoses produced by this test are always instances of attributing appendicitis to someone who does not, in fact, have it
Correct as mentioned above

C. all of the patients who are diagnosed with this test as having appendicitis do, in fact,have appendicitis
It doesn't say about the misdiagnosis. If the misdiagnosis is false positive, that will increase the necessary removals

D. every patient who is diagnosed with this test as having appendicitis has more than one of the symptoms generally associated with appendicitis
We are not talking about the symptoms associated with appendicities

E. the only patients who are misdiagnosed using this test are patients who lack one or more of the symptoms that are generally associated with appendicitis
It doesn't explain why unnecessary removals can be done by the doctors

1) Appendicitis is potentially fatal
2) 20% surgeries are unnecessary
3) New scan detects 98% cases correctly
4) => It leaves out 2% cases
5) Argument says that it is still OK to use and will still ensure that doctors won't skip surgery where it is needed.

This has to be based on the fact that 2% are always false positives (don't have appendicitis, but are detected as having it) rather than false negatives (have appendicitis, but not detected). This is because, if 2% are false negatives, these will potentially cause deaths. However if these are false positives, maybe 2% patients will have it removed when they didn't need to, but this is still better than 20% unnecessary surgeries, and as the surgery is safe, there is no hazard to these 2%.

So, (B) is correct.

Imagine there were 100 patients earlier out of whom 80 had appendicitis and 20 didn’t. But all 100 were given surgery (although only 80 were necessary and 20 were not necessary).

With the test that is 98% accurate, there are 2 extreme possibilities:

Case 1:

80 people have appendicitis; the test says all 80 have it.
20 people don’t have appendicitis; the test says 18 don’t have it and 2 have it. In this case 18 out of 20 unnecessary will be avoided and the doctors will still perform 82 surgeries (more than the necessary number 80). So this satisfies all the conditions. This case will be obtained when someone who doesn’t have appendicitis is diagnosed to have it. Option B says the same.

Case 2:

20 people don’t have appendicitis; the test says all 20 don’t have it.
80 people have appendicitis; the test says 78 have it and 2 don’t have it. In this case 2 necessary ones will also be avoided. The doctors will perform 78 surgeries (fewer than the necessary number 80). So this doesn’t satisfy any condition.

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 conclusion 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.

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

If the 2% error rate were due to the test not catching your appendicitis, 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.

Kudo it if you like the detailed explanation!

Can someone explain why 'C' is wrong

The passage ends with "since". Therefore a reason is required why the number of surgeries will go down (while the number of necessary surgeries will NOT go down).

Option C states that at present the diagnosed patients do all have appendicitis, that is there no wrong diagnosis for those who are actually positive. In future also there will be no wrong diagnosis for these actually positive patients. Therefore this is not the reason that the number of surgeries will go down.

If in future there are wrong diagnoses for these actually positive patients, (the positive patients will then be diagnosed as negative, i.e. not having appendicitis), then the number of surgeries will go down, but there is no indication that the new test will be carrying out such misdiagnoses. Hence C cannot be the answer.

Hi,
I know this CR question from prep has been discussed.

"Which of the following most logically completes the passage?

Appendicitis (inflammation of the appendix) is potentially fatal; consequently, patients with symptoms strongly suggesting appendicitis almost always have their appendix removed. The appropriate surgery is low-risk but performed unnecessarily in about 20 percent of all cases. A newly developed internal scan for appendicitis is highly accurate, producing two misdiagnoses for every 98 correct diagnoses. Clearly, using this test, doctors can largely avoid unnecessary removals of the appendix without, however, performing any fewer necessary ones than before, since ____________. "

"A. the patients who are correctly diagnosed with this test as not having appendicitis invariably have medical conditions that are much less serious than appendicitis

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

C. all of the patients who are diagnosed with this test as having appendicitis do, in fact, have appendicitis

D. every patient who is diagnosed with this test as having appendicitis has more than one of the symptoms
generally associated with appendicitis

E. the only patients who are misdiagnosed using this test are patients who lack one or more of the symptoms that
are generally associated with appendicitis "


However, I am quite confused b/w B and E.
Kindly note that I new to this forum,So pretty unsure about the posting rules.

Reagrds,
Abhishek Sinha

Hi Experts / sayantanc2k / VeritasPrepKarishma

Though I understand the solution, I am not too sure about choice C.

In my opinion choice C weakens the conclusion. If all the patients with append. do have app., then that would mean there are no patients who don't have append. but are diagnosed with append. But we are also told that 2% misdiagnosis is there. So this would mean that 2% cases would be of the patients who have append. but the tool misdiagnosed them. This would result in fewer surgeries than the necessary ones, and hence would not support the conclusion. Is my reasoning correct? Thanks very much!

SD

Choice (C) tells us that everyone who tests positive actually does have appendicitis. That means that the 2% comes from people who test negative. Most of those people probably do not have appendicitis, but there will be some people who test negative even though they have appendicitis.

Yes, this would result in fewer surgeries, but it would also mean that NECESSARY surgeries would not be performed. Say that five people test negative even though they have appendicitis. Obviously those people need the surgery to avoid potentially fatal consequences. But they won't get the surgery because they tested negative.

So the number of NECESSARY surgeries is likely to decrease... very bad news for the people in that 2% and, more importantly, it goes against the portion in bold:


I hope that helps!

Again, apologies if by now I sound like a broken record on this forum!
I am surprised by the quality of questions given by supposed English aficionados

1st a SC tip - since? There is no time connotation here - so since is definitely wrong to start with

Next coming to the question itself
Appendicitis does not have a real diagnosis (except for physical tests) - leading to unnecessary operation. This can be avoided by this internal scan because (lets not dive into numbers first - lets keep this at the back of our minds) - start looking at choices

A. the patients who are correctly diagnosed with this test as not having appendicitis invariably have medical conditions that are much less serious than appendicitis (off topic)

Looks like a SC question to me here - but lets not deviate
B. the misdiagnoses produced attributes appendicitis to someone who does not have it - so this one is suggesting that the misdiagnosis is there - Ok great - would that reduce surgeries/removals for sure? this could result in lowering numbers of unnecessary removals - or not - I am not too sure here ....could be maybe perhaps - convoluted logic - misdiagnosis in someone who does not have it will still result in unnecessary operation and removal?

C. all of the patients who are diagnosed with this test as having appendicitis do, in fact, have appendicitis - This is specific and accurate - not HR - not 1 word off - sticking to the plan...Now C says I am perfect - I am not guessing - the test predicts - options given - numbers decided accordingly. Next steps decided according to data

D. every patient who is diagnosed with this test as having appendicitis has more than one of the symptoms
generally associated with appendicitis (off topic)

E. the only patients who are misdiagnosed using this test are patients who lack one or more of the symptoms that
are generally associated with appendicitis " (off topic)

I am writing the below as it is important:
Test situation 2 mins in the test - I would definitely pick C - sticking to specifics? why should the GMAT prefer convoluted logic above simple straight logic is confusing.

Btw I got out of the 2 min mode and really looked into this question for 20 mins - still B did not come out as the better option over C

This slow and fast thinking is important as many know - eventually hopefully coinciding into one from practice

Any suggestions?


The above logic sounds like below
Trying to judge business smartness of an individual - clearly some test can without a measure of doubt pin down on the absolute IQ and EQ of a person. So one should most definitely pass the test. Else there is a possibility of being misdiagnosed as not fit for business.

I work very hard and thus I am smart - smartness is a necessary to being calculated by the amount of hours spent trying to be smart - though there is a test to prove it too (all the holes you will drill are intentional in this sentence)
vs
Idiocy levels are measured by a test - the test most definitely has shown that people who score above a threshold has been successful in business which requires smart skills. - I have repeatedly scored above that threshold (do be aware of the very convoluted logic here - along with multiple SC problems)
vs
Smartness skills as measured by a set of tests and other parameters suggest that this person is beyond smart. So fitness will be judged accordingly


There are subtle differences in all the above 3 choices too - Though have to say GMAT is taking me in loops and tests I have never faced in my smart/unsmart/smart-unsmart life!

AjiteshArun sir,
Why cannot option C be the answer?
If all the patients tested are diagnosed with appendicitis, then doesn't this reduce the unnecessary surgeries?

Please evaluate where I am going wrong.

Thanks

AjiteshArun sir, I have the same doubt as Karn. Could you please help if possible?

Hi rahulbiitk,

Let's take a quick look at the statement we need to strengthen:

There are two things we need to take care of here:
1. Largely avoid unnecessary removals
and
2. Not perform fewer necessary removals (we can ignore "than before" for the sake of convenience)

This is option C:

This option tells us that {every case that is identified} is {correctly identified}, but it does not tell us that {every case} is identified. For example, if 100 (out of 100,000) people actually have appendicitis, and this test identifies \(n\) cases, option C tells us that all \(n\) people do, in fact, have appendicitis. But it doesn't tell us that \(n=100\) (or, more accurately, it doesn't tell us that all those 100 people are within the set of people diagnosed with this test as having appendicitis). The test may be "catching" only 98 out of every 100 cases. The remaining people need surgery, but because the test doesn't catch all the cases, they won't get it.

In other words, when this test does identify appendicitis, it is correct, but we don't know whether it catches all cases of appendicitis. This means that there may be people with appendicitis who need surgery but don't get it, which means that, if doctors use this test, they may end up performing fewer necessary removals of the appendix.