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Main thing to notice here is that making a mistake "at least once"

Chance of a doctor making atleast one mistake = 1 - prob of making a mistake on (patient 1 or patient 2 or patient 3 ... or last patient)
This chance increases when prob of making a mistake on (patient1 or patient 2 or ... or last patient) decreases.

How does that decrease ?

- if you see less number of patients, then your chance of doing atleast one mistake is smaller than someone who sees far more patients. for ex, someone sees 10 patients vs someone who sees 1000 patients. The one seeing 10 patients may luck themselves out but when you see 1000 patients, you may likely make a mistake.
- Let's say number of patients are same for both cases but if you are seeing more risky patients than the other group, then also chance is higher to do a mistake
- Let's say number of cases are same and risky patients are same but you have some extra support that derisks you other than just experience ?

A. Between those 30 and below vs 35 and above, the difference could be due to any reason. Conclusion is concerned about 60 and above vs 35 and below.
B. Number of doctors in the group doesn't affect the risk of each doctor making atleast one mistake because we are talking in percentage terms not in absolute numbers. If it were absolute numbers, then more the number of doctors, the more the number of those that make mistake. But since we are talking in percentage terms here, it will nearly be the same assuming the risk per doctor is same.
C. Weakener. This decreases the risk per doctor for 60 and above and gives an alternate reason than mentioned in the conclusion.
D. Correct. If doctor in 60 and above age group treats far fewer people, then risk per each doctor goes down. So it is assumed that it is not the case.
E. There could be an age bracket for which the percentage is even smaller but for a different reason. So that doesn't necessarily break out argument or in other words not a necessary condition.
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Assumption:

Conclusion: Advanced experience and learning propensity possessed by doctors older than age 60, is the cause for the least error % when compared with doctors aged less than 35.

Premise: 10% avoidable errors for doctors below 30 & 7% errors for doctors between 30 and 35.

Assumption: To be found.

Answer: D.

Reason: If the aged doctors (>60) had treated way less number of patients than younger ones, then it's not possible that older docs have high experience & learnings than their younger peers.

Not the answer & reason:

C. This rather weakens the link. If older docs have treated, less high risky procedures than younger ones, then the learnings/experience can't be great relatively.
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Last year, 10 percent of doctors younger than 30 and 7 percent of doctors between the ages of 30 and 35, practicing in Darrenville, made at least one avoidable error during a medical procedure. On the other hand, only 2 percent of doctors 60 and older made such an error. These findings make it clear that the advanced experience and learned propensity for caution possessed by doctors in the 60 and older group make them far more reliable than younger doctors are.
s
Which of the following is an assumption on which the argument depends?

Conclusion : that advance experience ( >=60 ) years aged doctors are reliable and have low error during procedure

Use negation technique

(A) The difference between the error rate of doctors under 30 and of those between 30 and 35 cannot be attributed to the higher level of medical experience possessed by the older doctors. does not weaken the conclusion

(B) Doctors 60 years and above do make up a meaningfully larger fraction of physicians in Darrenville than doctors between the ages of 30 and 35 do. does not weaken the conclusion

(C) Doctors 60 years and above are more likely than are doctors 35 and younger to perform medical procedures under circumstances that significantly heighten the risk of errors. does not weaken the conclusion

(D) Doctors 60 years and above, on average, do , treat a considerably lower number of patients per year than doctors 35 and younger do. breaks the conclusion

OPTION D is correct

(E) For all age bracket is the error rate lower than it is for doctors 60 and older.
does not weaken the conclusion

OPTION D is correct
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For this one, it helped me better by just asking myself even before reading the options - what is the logical fallacy with this one? If doctors above 60 have a lower rate of errors than younger doctors, what if there are only two doctors who perform medical procedures in that age range - one made errors twice in the two procedures he did, with the other did not in 98 of the 98 procedures he did (that's 2% error rate). But half the doctors above 60 erred in their procedures, so how can anyone conclude older doctors are more reliable? With this thinking, I looked at the options:

A - This isn't a necessary assumption. Even if the doctor under 30 and those between 30 and 35 are not differentiated by a difference in experience, the comparison is between doctors aged 60 and above and younger doctors.

B - This can't be the assumption, perhaps its opposite could have been. To say there are few doctors above 60, in fact, in creates an impression that the sample size is too small to conclude 60+-ers are better doctors.

C. - This presents an alternative explanation for fewer errors among 60+ doctors. That they don't perform the kind of procedures that will result in risks, which the younger ones do just that. So this cannot be assumed.

D - My answer, IMO. If 60+ doctors treat a considerably lower number of patients, then such an error rate may not be attributed to experience / skillset. Let us say, doctors 35 and below treat an average of 10 patients each, while 60+ers treat just a patient each. Even a higher error percentage in this scenario would be offset by the exposure to number of patients. So to assume that this ISN'T THE CASE, becomes necessary.

E - A nice contender, but I wouldn't go for this simply because we already know those 35 and under make more errors, so even if the 35 to 60 bracket has a lower percentage than 60+ers, the fact remains the younger lot makes more errors, and it remains to be seen whether the 35 to 60 doctors can offset the errors made by their younger counterparts.




Bunuel
Last year, 10 percent of doctors younger than 30 and 7 percent of doctors between the ages of 30 and 35, practicing in Darrenville, made at least one avoidable error during a medical procedure. On the other hand, only 2 percent of doctors 60 and older made such an error. These findings make it clear that the advanced experience and learned propensity for caution possessed by doctors in the 60 and older group make them far more reliable than younger doctors are.

Which of the following is an assumption on which the argument depends?

(A) The difference between the error rate of doctors under 30 and of those between 30 and 35 can be attributed to the higher level of medical experience possessed by the older doctors.

(B) Doctors 60 years and above do not make up a meaningfully larger fraction of physicians in Darrenville than doctors between the ages of 30 and 35 do.

(C) Doctors 60 years and above are less likely than are doctors 35 and younger to perform medical procedures under circumstances that significantly heighten the risk of errors.

(D) Doctors 60 years and above, on average, do not, treat a considerably lower number of patients per year than doctors 35 and younger do.

(E) For no age bracket is the error rate lower than it is for doctors 60 and older.
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On analyzing the given options,

(A) This does not bring up the aspect of the 60 year old & above doctors who are at the crux of the argument. Eliminate
(B) This is not directly relevant to the argument because the argument talks about numbers within these groups & not the numbers of all doctors combined across groups. Eliminate
(C) This may be seen as a weakener as it may imply that the doctors above 60 are not performing enough operations of that nature & for that reason their % numbers are below the other groups. Eliminate
(D) This perfectly fits our argument & further strengthens the fact that doctors above 60 are more reliable as we are able to eliminate a control factor which could explain the lower % numbers in the doctors aged 60+. Keep
(E) The comparision is only between older & younger doctors only & not all the doctors. Middle aged doctors may have better numbers than both. Eliminate

The correct answer is option (D)
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Answer D-
Assumption MBT trues statement-
A. The conclusion of the author is about those >60 and not that BLANKET AGE INCREASE WILL INCREASE THE EXPERIENCE AND THEREFORE LESS CHANCES OF ERROR.
B. If they do- Then having less error rate will even bolster the argument. Therefore author is definitely not assuming that Doctors 60 years and above do not make up a meaningfully larger fraction of physicians in Darrenville than doctors between the ages of 30 and 35 do.
C. Is a perfect weakner that it is not the experience which is causing error but the kind of cases coming before the less experienced once.
D, Is definitely an assumption becuse if this is true then our conclusion can be shattered by the fact that- The error rate is more due to the Number of patients coming up are more.

Bunuel
Last year, 10 percent of doctors younger than 30 and 7 percent of doctors between the ages of 30 and 35, practicing in Darrenville, made at least one avoidable error during a medical procedure. On the other hand, only 2 percent of doctors 60 and older made such an error. These findings make it clear that the advanced experience and learned propensity for caution possessed by doctors in the 60 and older group make them far more reliable than younger doctors are.

Which of the following is an assumption on which the argument depends?

(A) The difference between the error rate of doctors under 30 and of those between 30 and 35 can be attributed to the higher level of medical experience possessed by the older doctors.

(C) Doctors 60 years and above are less likely than are doctors 35 and younger to perform medical procedures under circumstances that significantly heighten the risk of errors.

(D) Doctors 60 years and above, on average, do not, treat a considerably lower number of patients per year than doctors 35 and younger do.

(E) For no age bracket is the error rate lower than it is for doctors 60 and older.
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The core logic is: Older doctors have a lower error rate, therefore, they are more skilled/cautious and more reliable.

The author observes a correlation about age of doctors and error rate and jumps to a causal conclusion. For the correlation->causation, the author must have assumed that there are no other signficant difference rates that could explain the different error rates.

A. This choice talks about the difference between two younger groups <30 and b/w 30 and 35. The assumption is about this younger group with the older group. Incorrect.

B. The relative size of the group is irrelevant. We're only concerned about the rate of error. Incorrect.

C. If you negate this choice, it would actually weakens the argument. But, it doesn't break the conclusion. Incorrect.

D. If you negate this choice, it breaks the conclusion. If an older doctor only treats 10 patients per year and the younger ones treats 50, then the lower error rate must be due to lower workload and not necessarily because older doctors are more cautious. Correct.

E. It doesn't matter if there is some other group of doctors who have a relatively lower error rate than is with the older group. The comparison is b/w older group and younger group. Incorrect.
Bunuel
Last year, 10 percent of doctors younger than 30 and 7 percent of doctors between the ages of 30 and 35, practicing in Darrenville, made at least one avoidable error during a medical procedure. On the other hand, only 2 percent of doctors 60 and older made such an error. These findings make it clear that the advanced experience and learned propensity for caution possessed by doctors in the 60 and older group make them far more reliable than younger doctors are.

Which of the following is an assumption on which the argument depends?

(A) The difference between the error rate of doctors under 30 and of those between 30 and 35 can be attributed to the higher level of medical experience possessed by the older doctors.

(B) Doctors 60 years and above do not make up a meaningfully larger fraction of physicians in Darrenville than doctors between the ages of 30 and 35 do.

(C) Doctors 60 years and above are less likely than are doctors 35 and younger to perform medical procedures under circumstances that significantly heighten the risk of errors.

(D) Doctors 60 years and above, on average, do not, treat a considerably lower number of patients per year than doctors 35 and younger do.

(E) For no age bracket is the error rate lower than it is for doctors 60 and older.
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Evaluating options
A) The conclusion is comparing doctors of age 60 and older to younger doctors, not less than 30 and between 30-35 age group
B)This is not relevant as the argument is considering percentages and not actual numbers. So fraction of different age group doctors is already taken care of by the argument.
C)This weakens the conclusion. If doctors older than 60 are less likely to perform risky procedures, then the conclusion that older doctors are reliable, does not stand
D)This is an assumption that needs to be true. If the doctors above 60 years are performing considerably lower number of procedures on less number of patients, then the number of avoidable errors will also be low. This will break the reasoning to conclusion that older doctors are reliable
E)We are not concerned with any other age group commiting less number of errors
Bunuel
Last year, 10 percent of doctors younger than 30 and 7 percent of doctors between the ages of 30 and 35, practicing in Darrenville, made at least one avoidable error during a medical procedure. On the other hand, only 2 percent of doctors 60 and older made such an error. These findings make it clear that the advanced experience and learned propensity for caution possessed by doctors in the 60 and older group make them far more reliable than younger doctors are.

Which of the following is an assumption on which the argument depends?

(A) The difference between the error rate of doctors under 30 and of those between 30 and 35 can be attributed to the higher level of medical experience possessed by the older doctors.

(B) Doctors 60 years and above do not make up a meaningfully larger fraction of physicians in Darrenville than doctors between the ages of 30 and 35 do.

(C) Doctors 60 years and above are less likely than are doctors 35 and younger to perform medical procedures under circumstances that significantly heighten the risk of errors.

(D) Doctors 60 years and above, on average, do not, treat a considerably lower number of patients per year than doctors 35 and younger do.

(E) For no age bracket is the error rate lower than it is for doctors 60 and older.
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Bunuel
Last year, 10 percent of doctors younger than 30 and 7 percent of doctors between the ages of 30 and 35, practicing in Darrenville, made at least one avoidable error during a medical procedure. On the other hand, only 2 percent of doctors 60 and older made such an error. These findings make it clear that the advanced experience and learned propensity for caution possessed by doctors in the 60 and older group make them far more reliable than younger doctors are.

Which of the following is an assumption on which the argument depends?

(A) The difference between the error rate of doctors under 30 and of those between 30 and 35 can be attributed to the higher level of medical experience possessed by the older doctors.

(B) Doctors 60 years and above do not make up a meaningfully larger fraction of physicians in Darrenville than doctors between the ages of 30 and 35 do.

(C) Doctors 60 years and above are less likely than are doctors 35 and younger to perform medical procedures under circumstances that significantly heighten the risk of errors.

(D) Doctors 60 years and above, on average, do not, treat a considerably lower number of patients per year than doctors 35 and younger do.

(E) For no age bracket is the error rate lower than it is for doctors 60 and older.
Age < 30 years -> 10% errors
30 years <= Age < 35 --> 7% errors
Age > 60 years --> 2% errors

Experienced doctors are more reliable than young doctors

A -> To what the errors are attributed is not required as a conclusion
B -> The error percentages even with not a meaningful count is not an assumption required here
C -> This may or may not be true hence is not needed as an assumption
D -> This is required as an assumption otherwise the whole argument would be skewed and not valid
E -> This may not be a required assumption. Other age brackets are not discussed.

Option D
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Doctors aged 60 and older are far more reliable than younger doctors because of their experience and caution.

The Argument assumes that the lower rate of error among 60+ is not due to their reliability ;
not because they - handle fewer risky cases

Option A : wrong subgroup comparisons.
Option B : Percentages already account for group size .
Option C : Undermine the conclusion.
Option D : Do not treat fewer patients per year , Amount is same therefore experience factor comes into play for 60+.✅
Option E : Too Strong - The Argument doesn't need 60+ to be the best , Only better than younger doctors.
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Doctor Error Rate = # Doctors committing errors/# Doctors

#Doctos = #Doctors committing errors + #Doctors not committing errors + #Doctors not treating anyone

Doctor Error Rate can be low if Denominator is large (#Doctors not treating anyone >> #Doctors not committing errors)
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IMO E.....A very close question.....Lets see...

A. The difference between error rate of below 30 and 30-35 can be attributed...even if it cannot be attributed....we are talking about difference from 7 or 10 to 2.......So negation of this doesnt impacts the conclusion

B. Do not make up a meaningfully larger fraction ..first of all I have a problem with 'physicians'..is it talking about the doctors......If yes...physicians and doctors are just same people here..
Then.....The negation goes....yes they make up large fraction of doctors than 30-35 do ....but there is still no comparison with under 30..they could make even a larger fraction.....

but if physician here is a subset ....then the answer is irrelevant ....


C. This is a weakener....assumption should have been equally likely or not less likely .....

D...Lets assume a case of negating this option....lets assume that they do in fact treat a lower number of patients....
Doctors age...60+ ..Number of doctors..100.Medical procedure...1 per year per doctor....Error is 2%..so 2 procedures wrong...
Doctors age 35 or less...Number of doctors...100..Medical procedure 2 per year per doctor....total is 200 ...Error is 7 or 10%..lets assume even 7% ....so still larger medical procedures wrong by these doctors.... This infact seems a strenghtener


E....Now the negation of this breaks the logic that the author is using....suppose age bracket....35-50 have error rate of 0.5%..then what? then the error rates go like 10%..7%..0.5% and then rise 4 times that is 2% in 60+.....so the logic that is being used to support the conclusion is wrong and the conclusion breaks with this negation.






Bunuel
Last year, 10 percent of doctors younger than 30 and 7 percent of doctors between the ages of 30 and 35, practicing in Darrenville, made at least one avoidable error during a medical procedure. On the other hand, only 2 percent of doctors 60 and older made such an error. These findings make it clear that the advanced experience and learned propensity for caution possessed by doctors in the 60 and older group make them far more reliable than younger doctors are.

Which of the following is an assumption on which the argument depends?

(A) The difference between the error rate of doctors under 30 and of those between 30 and 35 can be attributed to the higher level of medical experience possessed by the older doctors.

(B) Doctors 60 years and above do not make up a meaningfully larger fraction of physicians in Darrenville than doctors between the ages of 30 and 35 do.

(C) Doctors 60 years and above are less likely than are doctors 35 and younger to perform medical procedures under circumstances that significantly heighten the risk of errors.

(D) Doctors 60 years and above, on average, do not, treat a considerably lower number of patients per year than doctors 35 and younger do.

(E) For no age bracket is the error rate lower than it is for doctors 60 and older.

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Last year, 10 percent of doctors younger than 30 and 7 percent of doctors between the ages of 30 and 35, practicing in Darrenville, made at least one avoidable error during a medical procedure. On the other hand, only 2 percent of doctors 60 and older made such an error. These findings make it clear that the advanced experience and learned propensity for caution possessed by doctors in the 60 and older group make them far more reliable than younger doctors are.

Which of the following is an assumption on which the argument depends?

(A) The difference between the error rate of doctors under 30 and of those between 30 and 35 can be attributed to the higher level of medical experience possessed by the older doctors. (It doesn't discuss about 60+ aged doctors) Wrong
(B) Doctors 60 years and above do not make up a meaningfully larger fraction of physicians in Darrenville than doctors between the ages of 30 and 35 do. Wrong
(C) Doctors 60 years and above are less likely than are doctors 35 and younger to perform medical procedures under circumstances that significantly heighten the risk of errors.
(Only explain why their error rate is low and it doesn't connect to them being more reliable and more experienced) Wrong
(D) Doctors 60 years and above, on average, do not, treat a considerably lower number of patients per year than doctors 35 and younger do.
(If they treat a lower number of patients per year then it means their higher experience and skillset do not play a role in low error rate and negating this option also weakens the conclusion) Correct

(E) For no age bracket is the error rate lower than it is for doctors 60 and older. (Not an assumption) Wrong

D
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option D is correct because the sample size should be similar for comparing the results.
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Here, the proportion of doctors making at least 1 mistake is categorized age wise and conclusion made that age gives experience to avoid such error. This applies to 60 or older vs all younger.
Assumption is that all cases handled by age groups across are similar in terms of risk, environment.

This makes D as best choice, imo.

Bunuel
Last year, 10 percent of doctors younger than 30 and 7 percent of doctors between the ages of 30 and 35, practicing in Darrenville, made at least one avoidable error during a medical procedure. On the other hand, only 2 percent of doctors 60 and older made such an error. These findings make it clear that the advanced experience and learned propensity for caution possessed by doctors in the 60 and older group make them far more reliable than younger doctors are.

Which of the following is an assumption on which the argument depends?

(A) The difference between the error rate of doctors under 30 and of those between 30 and 35 can be attributed to the higher level of medical experience possessed by the older doctors.

(B) Doctors 60 years and above do not make up a meaningfully larger fraction of physicians in Darrenville than doctors between the ages of 30 and 35 do.

(C) Doctors 60 years and above are less likely than are doctors 35 and younger to perform medical procedures under circumstances that significantly heighten the risk of errors.

(D) Doctors 60 years and above, on average, do not, treat a considerably lower number of patients per year than doctors 35 and younger do.

(E) For no age bracket is the error rate lower than it is for doctors 60 and older.

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Bunuel
Last year, 10 percent of doctors younger than 30 and 7 percent of doctors between the ages of 30 and 35, practicing in Darrenville, made at least one avoidable error during a medical procedure. On the other hand, only 2 percent of doctors 60 and older made such an error. These findings make it clear that the advanced experience and learned propensity for caution possessed by doctors in the 60 and older group make them far more reliable than younger doctors are.

Which of the following is an assumption on which the argument depends?

(A) The difference between the error rate of doctors under 30 and of those between 30 and 35 can be attributed to the higher level of medical experience possessed by the older doctors.

(B) Doctors 60 years and above do not make up a meaningfully larger fraction of physicians in Darrenville than doctors between the ages of 30 and 35 do.

(C) Doctors 60 years and above are less likely than are doctors 35 and younger to perform medical procedures under circumstances that significantly heighten the risk of errors.

(D) Doctors 60 years and above, on average, do not, treat a considerably lower number of patients per year than doctors 35 and younger do.

(E) For no age bracket is the error rate lower than it is for doctors 60 and older.

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In this question the comparison only make sense if all groups are exposed to roughly the same number of chances to make errors.
If this were not true - if older doctors treat far fewer patients - then:
They would have fewer opportunities to make an error and the conclusion would collapse.

Therefore, option D is the correct.
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The argument attributes the lower error rate in the older group to experience and caution rather than other factors.
The argument assumes there are no confounding factors (like case difficulty, number of patients, etc.) that explain the difference in error rates, other than experience and caution.

A Talks about difference within younger groups. This is irrelevant to conclusion about older vs younger. Not needed for argument.

B Fraction of physicians in Darrenville by age group: it's not relevant to per-doctor error rates.

C If this were false (older doctors do perform in high-risk circumstances just as often or more), that could support the conclusion, but actually the argument's conclusion requires that older doctors do not simply have easier cases.

D If older doctors treat many fewer patients, they have fewer opportunities to make errors, so lower error percentage could be due to less exposure, not greater reliability.

E It's irrelevant. Argument is about older vs younger, not other age groups.


IMO D
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