#21 - When a person with temporal lobe epilepsy is having an

[Administrator]

Complete Question Explanation

Must Be True. The correct answer choice is (D)

The data says: If a person with TLE has an epileptic seizure, the brain's TL produces abnormal electrical impulses which can often be detected by EEG.

There are two possible problems with the EEG test. One is the "false positive": the EEG might detect abnormal electrical impulses when there's not actually any abnormal impulses, or there are abnormal impulses but there is no seizure.

Another problem with the EEG test is the "false negative": the EEG might fail to detect abnormal electrical impulses when they are actually present, caused by a seizure.

The last sentence of the stimulus suggests that a positive EEG reading is a reasonably reliable indicator of TLE … and what goes in the blank? A natural concept to go in the blank is: there's a small chance that it might just be a false positive.

Answer choice (A): If a positive EEG reading indicates 50% probability of TLE and 50% probability of no TLE, then this is not a "reasonably reliable" test, as the stimulus said. So this answer choice cannot be correct.

Answer choice (B): The stimulus never discussed other forms of epilepsy, so this answer choice cannot be correct.

Answer choice (C): We know nothing about the frequency of false positives vs. false negatives.

Answer choice (D): This is the correct answer choice. This answer choice captures the "false negative" phenomenon as discussed above.

Answer choice (E): If both a positive EEG reading and a negative EEG reading give exactly the same information about the likelihood of TLE, then running the test is completely pointless. We don't have any information from the stimulus to support this.

[acp25]

Hi,

I read the explanation and I just don't get it. I understood the stimulus up until "Therefore..." Which part of the stimulus did the two possible EEG problems come from?

[Jay Donnell]

Hi acp25!

This is a nasty MBT fill in the blank style question, and I'm happy to help clear it up!

The key behind the whole question comes from the following statement: "...produces abnormal electrical impulses, which can often, but not always, be detected through a test..."

This means that the EEG test can't always catch the incidence of temporal epilepsy, so if a test failed to register as a positive result, it doesn't mean that the patient doesn't suffer from temporal epilepsy.

The concept illustrated here involves what is often referred to as a Confusion Matrix, which entails the four possible results of a test for a given condition.

Let's say that we are developing a test that identifies whether or not a patient has the gene for mutant super powers. Okay, you got me, I am not-so-secretly very excited for Avengers Endgame to come out next week!

So, if we ran this test on a patient we have only four possible outcomes:

True Positive: The test found the patient to have the mutant gene, and the patient actually does have the gene.
True Negative: The test found the patient to not have the mutant gene, and the patient actually doesn't have the gene.

False Positive: The test found the patient to have the mutant gene, but the patient actually does not have the gene.
False Negative: The test found that the patient did not have the mutant gene, but the patient actually does have the gene.


The risk in this particular stimulus involves a False Negative. Since we know that the EEG test can "often, but not always detect" temporal lobe epilepsy, it's possible that a test that shows up as negative could be mistaken, and the patient does in fact have the condition.

We know that if the test results come out as positive it IS a trustworthy indicator of the presence of the condition (True Positive), but that there remains a potential risk factor of a False Negative diagnosis.

Just because the test was negative it doesn't mean the patient does not have the condition, it simply could have been one of the instances in which the test was simply unable to detect the presence of temporal lobe epilepsy in the patient.


I hope that helps to clear it up, happy Friday to you!

[chiickenx]

Hi, while i got the question correct, I don't quite exactly understand the argument... Can someone please further elaborate? Moreover, can you please check my blind review of this question? My blind review is as follows:

A.
Idk… what if AEP in temporal lobe most often occurs with TLE. If this is the case, chances are pretty high that a person has TLE. And thus, it is not “just as reliable.” As such, this AC is not supported.
B.
Idk anything abou other forms of epilepsy.
C.
Idk anything about the frequency of error….
D.
Yeah… because a person could have TLP, but is not undergoing a seizure…
E.
Honestly, I wanted to choose this because I have no clue how the in the world the author concluded that positive EEG was a reliable indicator of TLP… The thing that helped me eliminate this AC was the phrase “just as reliable.”The author needs to tell us that nothing else could have caused or is sufficient for AEP in the temporal lobe… but… this would go against the stimulus, which says that a positive reading is “reasonably reliable”... because it is not true that a positive is a reasonably reliable indicator of TLP if a negative reading is just as reasonably reliable… at that point, its like why do the test if there can only be two results…

[KelseyWoods]

Hi Chiickenx!

Your reasoning with regard to the answer choices seems pretty spot on! Let's see if we can clear up some of your confusion with this stimulus to make you more confident in your correct answer.

This stimulus gives us a fill-in-the-blank style Must Be True question. Essentially, that means that the author has provided us with all of the premises, and we must determine what conclusion we can support with those premises. So let's breakdown those premises:

P1: During a TLE seizure, electrical impulses are produced
P2: These electrical impulses can often, but not always, be detected with an EEG

The next statement, immediately following the "Therefore," gives us information about positive readings (reasonably reliable). So basically it helps guide us in the direction of making a conclusion about negative readings because we already have a statement about positive readings.

So if the electrical impulses produced by TLE seizures cannot always be detected with an EEG, that means that sometimes a person might be having a TLE seizure that goes undetected by the EEG. Therefore, a negative reading on an EEG is not a guarantee that the person is not undergoing a TLE seizure, because, again, the EEG might just not be detecting those electrical impulses

Hope this helps!

Best,
Kelsey