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

Question

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

Can someone also explain what does the last line mean?

ruda · Accepted Answer

I read this in other forum and it help me understand better the solution. See if helps anyone:

"Complete the passage questions are like inference questions. You will most likely have to put in the correct conclusion or else (as here) a correct piece of evidence that would logically support the conclusion. As with other inference questions, the best approach is to follow the gist of the passage, make a deduction and scan for a match.

Here, the author is arguing that the scan will obviate the need for surgeons to perform unnecessary appendectomies. Really? Let's examine what we have learned about the scan: the misdiagnosis rate is 2%. But are the misdiagnoses false positives or false negatives? A false positive is where the scan says you have appendictis when you don't while a false negative is when the scan fails to pick up that a patient has appendictis when in fact they do. False positives are not risky here b/c if a person who doesn't have appendictis gets his/her appendix removed, its no big deal. On the other hand, false negatives are very risky b/c if a person who has appendicitis doesn't get his/her appendix removed, then they may die. So, in order for the author's conclusion to be correct, the kind of misdiagnoses the scan makes must be false positives and not false negatives. That would be the piece of evidence that would support the conclusion (we know we want to put in some evidence here b/c the passage ends with "since'). That is our deduction, and now we scan for a match....choice B."

-> I think the statement we need to fill is a piece of information that will guarantee that they will perform "ALL THE NECESSARY" operations, in this case even when is a misdiagnoses. I think C does not clear that as well as B. C lives room to ask "what about the misdiagnoses?"

Hope it helps!

sayantanc2k · Answer

There is no need to open a new topic - just add your comment in the previous thread. For this one, I have merged your new topic with the previous one.

Coming to your query:

Misdiagnosis can be of two types:
False positive: A person who does not have appendicitis is identified as having appendicitis.... this leads to unnecessary operation.
False negative: A person who has appendicitis is identified as not having appendicitis.... this leads to faulty release of the patient without operation.

Option B implies that the misdiagnoses are always "false positive" type. There is no chance of getting a "false negative", i.e. there are 2% false positive misdiagnoses and 0% false negative misdiagnosis.

The latter implies that there is no way that that a person who has appendicitis is identified as not having appendicitis. Hence necessary operations are not going to be reduced, since the test does not produce a single case of "false negative".

On the other hand because the test is 98% accurate (only 2% "false positive" misdiagnosis), there will be drastic reduction of unnecessary operations (though they cannot be eliminated altogether).

KASSALMD · Answer

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.

incognito1 · Answer

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.

calvinhobbes · Answer

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.

kraizada84 · Answer

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..!!

Hence B.

Hope this helps..!!

eybrj2 · Answer

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.

kinjiGC · Answer

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

HardWorkBeatsAll · Answer

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.

Pronz · Answer

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!

sairam595 · Answer

Can someone explain why 'C' is wrong

sayantanc2k · Answer

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.

sdlife · Answer

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

GMATNinja · Answer

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!

krndatta · Answer

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

rahulbiitk · Answer

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

AjiteshArun · Answer

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.

Raman109 · Answer

We are looking here for a strengthener. The main concern is the 2% misdiagnosis. Suppose the 2% misdiagnosis leads to missing the people who have appendicitis - it's a disaster. But if they are people who don't have it, the test misdiagnoses them as having it, at best, no harm to them.  
Option Elimination -

(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 -  other medical conditions are out of scope.

(B) the misdiagnoses produced by this test are always instances of attributing appendicitis to someone who does not, in fact, have it -  per our pre-thinking.

(C) all of the patients who are diagnosed with this test as having appendicitis do, in fact, have appendicitis -  we are concerned about misdiagnosis, out of scope.

(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 concerned about misdiagnosis, out of scope.

(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 -  if they lack one or more symptoms, does it mean they don't have it? We don't know. Maybe they still have it, and other symptoms show the appendicitis. Distortion.

ChiranjeevSingh · Answer

Passage Analysis

Appendicitis (inflammation of the appendix) is potentially fatal;

A disease, appendicitis, can lead to death.

consequently, patients with symptoms strongly suggesting appendicitis almost always have their appendix removed.

As a result, patients who have symptoms that strongly suggest the presence of the disease almost always have their appendix removed. At this stage, I observe that the statement is talking about patients with symptoms that  strongly suggest  the presence of the disease. The statement is not talking about patients where we are confirmed that the patient has the disease. Still, these patients almost always have their appendix removed. That's interesting.

The appropriate surgery is low-risk but performed unnecessarily in about 20 percent of all cases.

The surgery for the removal of the appendix has a low risk but is performed unnecessarily in about 20% of the cases. This means that in 20% of the cases, the surgery is not really required.

Why is it not required? It could be that the patient does not have the disease or that the disease can be cured without the surgery. But so far, the passage hasn't talked about any cure as such; it just talks about the disease and the surgery. So at this stage, it seems like in 20% of the cases there was no disease, but the patient had symptoms that suggested the presence of the disease.

A newly developed internal scan for appendicitis is highly accurate, producing two misdiagnoses for every 98 correct diagnoses.

Okay, so now we have a new technology, a new scan that is highly accurate in determining whether a person has appendicitis. This scan produces only two misdiagnoses for every 98 correct diagnoses. This means that the error rate is just 2%. This is sharply lower than the 20% figure quoted above, so I can already see that the percentage of surgeries performed unnecessarily will go down substantially if this scan is used.

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

The statement presents the  conclusion  of the argument using the above premises. It says that by using this test, this new scan can largely avoid unnecessary removals of the appendix. This makes sense because the error rate is down to 2%. But the  conclusion  also adds  without performing any fewer necessary ones . This means that whenever the surgery is necessary, we don't want to avoid it.

It should not happen that a person who has the disease is diagnosed as not having the disease, so that person doesn't have the surgery. In that case, as the passage already says, the person can die. So the  conclusion  says that using the test will largely avoid unnecessary removals, but it will not lead to an issue where a person who requires surgery is misdiagnosed.

The sentence ends with the word  since , so we are looking for an option that  supports  this  conclusion . As I think about it, the first part of the  conclusion  directly follows from the statistic that the error rate is 2%, so it should largely avoid unnecessary removals. But for the second part, we may need some  support  because it's saying  without performing any fewer necessary ones . So we don't want any reduction, not even a 1% reduction, in the performing of necessary surgeries.

Options Evaluation

(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

Incorrect.    This option talks about the patients who have the new scan and who are diagnosed as not having the disease. These patients have other less serious medical conditions. This option is  completely irrelevant  because we are not concerned about whether the patients have other diseases or not.

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

Correct.    This option talks about the misdiagnoses or the errors made by this test. It says that the misdiagnoses are always those cases in which a person does not have the disease, but the scan says that the person has the disease. So all the errors are those errors in which we will have an unnecessary surgery.

This also means that there is no error in cases where the person actually has a disease, but the scan says that they don't have the disease. This option is eliminating the case in which the scan leads to the avoidance of a necessary surgery. So this option directly  supports  the  conclusion , which was saying that using this test will not lead to any fewer necessary surgeries. This is the  correct  answer.

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

Incorrect.    This option talks about those patients who are diagnosed by the scan as having the disease. The option says that all of these patients actually have the disease. This means that whenever the scan says the person has a disease, the scan is right. This also means that the scan is wrong only in those cases in which the scan says the person does not have the disease.

Think about it. The scan says the person does not have the disease, and the scan is wrong. This means that the person actually has the disease. So you have a case in which the person has a disease, but he will not get the surgery because the scan is saying he doesn't have the disease. So actually, this option is saying there will be an absence of some necessary surgeries. This option is  going against the conclusion .

Let's consider the following variation of the option.

(C1): all of the patients undergoing the test who have appendicitis are diagnosed as having appendicitis

This variation of the option  supports  the  conclusion  by saying that everyone who has the disease is diagnosed as having the disease. So this  supports  that there will not be any absence of necessary surgeries. In a way, both option (B) and this variation mean the same thing. Of course, you cannot have both of these options together, but for learning's sake, we can understand that this variation would have been correct.

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

Incorrect.    This option talks about patients who have been diagnosed by the test as having the disease. It says that those patients have more than one symptom associated with the disease. But does having more than one symptom mean that they have the disease? If so, then the option is saying the same as what option (C) is saying. So in any case, this option goes in the  opposite direction  to the  conclusion .

The direction is  opposite , but option (C) is much  stronger  because that option very clearly states that those persons have the disease, whereas this option is just saying that they have more than one symptom. In that case, there is no surety whether they have the disease or not.

(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

Incorrect.    This option talks about the set of patients who are misdiagnosed using this test. It says that only those people are misdiagnosed who do not have some of the symptoms. So let's say there are 10 symptoms associated with the disease, and let's say a person has all 10 symptoms. Then, according to this option, this person will not be misdiagnosed. Only people with nine or fewer symptoms will be misdiagnosed.

But can we really say whether those people having nine or fewer symptoms actually have the disease or not? Not really. This option doesn't really tell me which patients are being misdiagnosed—patients having the disease or patients not having the disease. To  support  the  conclusion , we need to say that the patients being misdiagnosed are those patients who do not have the disease, but this option does not really say that. This is  incorrect .

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

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

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