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dcummins
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10 Jun 2019, 20:58
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C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
65%
(hard)
Question Stats:
55% (01:52) correct
45%
(02:02)
wrong
based on 1327
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Which of the following best completes the passage below?
A study was recently conducted to determine whether power lines caused some kind of negative health effects. The researchers surveyed everyone living within 200 meters of highvoltage power lines over a 15-year period and looked for statistically significant increases in rates of over 1000 ailments. The study found that the incidence of childhood leukaemia was four times higher among those who lived closest to the power lines. However, this statistic by itself should not be a cause for alarm, because__________________________.
(A) childhood leukemia can also be caused by other genetic factors
(B) another study has found that most of the children who suffer from childhood leukemia stay far away from power lines
(C) the number of potential ailments, that is, over 1000, was so large that it created a high probability that at least one ailment would exhibit statistically significant difference just by chance alone
(D) there was no significant correlation between the other 999 diseases and how close to power lines a person stayed
(E) childhood leukaemia, unlike leukaemia in adults, can be cured by medicines and therapy and is rarely fatal
A study was recently conducted to determine whether power lines caused some kind of negative health effects. The researchers surveyed everyone living within 200 meters of highvoltage power lines over a 15-year period and looked for statistically significant increases in rates of over 1000 ailments. The study found that the incidence of childhood leukaemia was four times higher among those who lived closest to the power lines. However, this statistic by itself should not be a cause for alarm, because__________________________.
(A) childhood leukemia can also be caused by other genetic factors
(B) another study has found that most of the children who suffer from childhood leukemia stay far away from power lines
(C) the number of potential ailments, that is, over 1000, was so large that it created a high probability that at least one ailment would exhibit statistically significant difference just by chance alone
(D) there was no significant correlation between the other 999 diseases and how close to power lines a person stayed
(E) childhood leukaemia, unlike leukaemia in adults, can be cured by medicines and therapy and is rarely fatal
21 Jun 2019, 09:56
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Let's work with an easier example: if we roll one die one time, our chances of getting a 3 are relatively low (~17%). If we roll two dice one time, our chances of getting at least one 3 are significantly higher (~30%). If we roll ten dice one time, our chances of getting at least one 3 are pretty good (~84%). If we roll a hundred dice one time, we're extremely likely to get at least one 3 (>99.99%). So even though the probability of getting a 3 on any one die isn't super high, the more dice we roll, the more likely at least one of the dice will give us a 3.
Bringing it back to this problem: it's not very likely that the survey is going to give us a false result for any one ailment. However, we did test a thousand of them. So even though the probability of getting an incorrect statistic for any one ailment is low, the more statistics we test, the more likely at least one of them will give us a false result. In other words, because we tested so many ailments, there's a pretty high likelihood that the result for one of the ailments is false — that an ailment shows a statistically significant difference near power lines vs. away from power lines when it actually shouldn't. We only saw one statistically significant difference (in childhood leukemia), so it's likely to be that false result.
Bringing it back to this problem: it's not very likely that the survey is going to give us a false result for any one ailment. However, we did test a thousand of them. So even though the probability of getting an incorrect statistic for any one ailment is low, the more statistics we test, the more likely at least one of them will give us a false result. In other words, because we tested so many ailments, there's a pretty high likelihood that the result for one of the ailments is false — that an ailment shows a statistically significant difference near power lines vs. away from power lines when it actually shouldn't. We only saw one statistically significant difference (in childhood leukemia), so it's likely to be that false result.
11 Jun 2019, 10:42
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D is a really great example of answering the wrong question. In this question, we're filling in a premise for the conclusion (that we shouldn't be alarmed about the statistic), so we essentially have a strengthen question. This means we're looking for an answer choice that gives a reason we shouldn't be alarmed that the study shows that children living near power lines have a 4x rate of leukemia.
D is tempting — it's a relief to know that the other 999 ailments aren't a concern! We would definitely be more alarmed by the study if more ailments showed statistically significant correlations. However, does this choice answer our question? If other ailments aren't impacted, does that mean the crazy high rate of childhood leukemia shouldn't alarm us? "4 times as many children are going to get blood cancer, no need to be alarmed!" ... that just doesn't sound right. While the info in this answer choice is good, and does relate to how concerning the results of this study are as a whole, it doesn't give a reason that the leukemia statistic itself shouldn't alarm us.
C, on the other hand, tells us that the leukemia statistic is very likely to be inaccurate — that it was a false positive, and children who live near power lines aren't actually more likely to get leukemia. If the statistic is inaccurate, we don't need to be alarmed about it. This answers the correct question, and thus is our answer.
The "good information, wrong question" answer choice is really common on the GMAT CR (and RC!). We can avoid it by reminding ourselves of what we want the answer choice to do as we work through our options.
D is tempting — it's a relief to know that the other 999 ailments aren't a concern! We would definitely be more alarmed by the study if more ailments showed statistically significant correlations. However, does this choice answer our question? If other ailments aren't impacted, does that mean the crazy high rate of childhood leukemia shouldn't alarm us? "4 times as many children are going to get blood cancer, no need to be alarmed!" ... that just doesn't sound right. While the info in this answer choice is good, and does relate to how concerning the results of this study are as a whole, it doesn't give a reason that the leukemia statistic itself shouldn't alarm us.
C, on the other hand, tells us that the leukemia statistic is very likely to be inaccurate — that it was a false positive, and children who live near power lines aren't actually more likely to get leukemia. If the statistic is inaccurate, we don't need to be alarmed about it. This answers the correct question, and thus is our answer.
The "good information, wrong question" answer choice is really common on the GMAT CR (and RC!). We can avoid it by reminding ourselves of what we want the answer choice to do as we work through our options.
