enthu
Forum Junior
Topics: 14
Posts: 42
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16. The table shows survival information for patients who had an operation for a particular form of cancer:
Interval Patients at the Beginning of the Interval Patients Who Died During the Interval Patients Surviving This Interval (%)
0-1 year 500 100 80
1-2 years 400 50 87.5
2-3 years 350 35 90
3-4 years 315 31 90
Based on this information, if a patient survives for 1 year, which of the following is the probability that he or she will survive for 4 years?
A. (0.875 - 0.8) X 0.9 = 0.0675
B. 0.8 X 0.875 X 0.9 X 0.9 = 0.567
C. 0.875 X 0.9 = 0.7875
D. 0.875 X 0.9 X 0.9 = 0.7088
E. 0.9
F. 0.9 X 0.875 = 0.025
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| srinivas
Forum Newbie
Topics: 0
Posts: 7
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the answer is d
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| rthungat
Forum Newbie
Topics: 4
Posts: 11
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d
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| enthu
Forum Junior
Topics: 14
Posts: 42
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yes its D.
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| paba
Forum Senior
Topics: 15
Posts: 57
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can anyone explain
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| pearljam59
Forum Guru
Topics: 120
Posts: 273
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OK I JUST took NBME form 3 and this question is fresh in my mind. I was not sure if my reasoning was correct but all the "D's" in the forum may have solidified it.
I used minimal knowledge of statistics to answer this. Rather, think of the probability of things happening...
The probability of staying alive after 2nd year is 87.5. The probability of third is 90 and the probability of fourth year alive is 90 again. So the probability of ALL three happening is figured out by the MULTIPLICATION rule! Remember to be alive after four years the two previous probabilities must be attained.
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| mosfet
Forum Newbie
Topics: 1
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why can't it be B? don't you have to multiply 0.8 also
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| pearljam59
Forum Guru
Topics: 120
Posts: 273
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No it cannot be B because the question is basing on the probability of survivng for 4 years AFTER already surviving the first year. If the ? asks for survival of 4 years the day after surgery then you would include it.
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