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.