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Short-Term Actuarial Math Old Exam C Forum

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Old 01-27-2015, 03:09 PM
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trondogss trondogss is offline
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Default Kaplan-Meier/Nelson Aalan Question Interpretation

I keep making this mistake, but maybe the wording is misleading. Here is what I get tripped up on:

Given:
10 people are no longer in the study lasting this many weeks (1, 1, 1, 2, 2, 3, 4, 6, 11, 30)

I'm good with this, here is what I get tripped up on:

10 people are currently in the study for the following number of weeks (0, 0, 1, 1, 2, 5, 5, 8, 20, 35)

SO...here is how I translate that last statement, these members are "currently" not out of the study, and the times given are how long they have been in the study...meaning these people are "new" to the study at times (End point minus given)

In this problem, I had them "new" at times (35, 35, 34, 34, 33, 33, 30, 30, 27, 15, 0)

This means that my risk set at time 0 is 11 (the 0 "new" and the 10 that died during study). The solution for this problem has a risk set of 20 at time 0.

Is the wording strange, or am I overanalyzing the givens.

This is Mahler Exam 15 Question 23 in the 2015 Exam set.

Thanks in advance.
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Old 01-27-2015, 03:19 PM
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Re-reading the solution, it makes more sense to me in that this is a disability study, and the 2nd given set is "censored from above".

If they do not use the term "disability" in the wording of the question, and just use the term "study" as I did above, then am I supposed to assume it is censored from above, or treat it like a mortality study assume they are still in the study?

Thanks in advance.
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Old 01-27-2015, 05:03 PM
Howard Mahler Howard Mahler is offline
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Alan has been in the disability study for 10 weeks.
For example, he entered 10 weeks ago and is still in the study today, when the study ends.
We do not know how long Alan will remain disabled beyond 10 weeks, because the study has ended.

Beth has been in the mortality study for 60 years since birth.
For example, she entered 60 years ago and is still in the study today, when the study ends.
We do not know how long Beth will remain alive beyond 60 years, because the study has ended.

In the first case, we are measuring when someone became disabled.
In the second case, we are measuring from when someone was born.
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Old 01-27-2015, 06:49 PM
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Quote:
Originally Posted by Howard Mahler View Post
Alan has been in the disability study for 10 weeks.
For example, he entered 10 weeks ago and is still in the study today, when the study ends.
We do not know how long Alan will remain disabled beyond 10 weeks, because the study has ended.

Beth has been in the mortality study for 60 years since birth.
For example, she entered 60 years ago and is still in the study today, when the study ends.
We do not know how long Beth will remain alive beyond 60 years, because the study has ended.

In the first case, we are measuring when someone became disabled.
In the second case, we are measuring from when someone was born.
So then with the 1st case, and 2nd given (from the original post):

"10 people are currently in the study for the following number of weeks (0, 0, 1, 1, 2, 5, 5, 8, 20, 35)"

Wouldn't that mean that the people in this bucket did not enter the study until time 35 minus given, so times (35, 35, 34, 34, 33, 33, 30, 30, 27, 15, 0)?

Why would I take the given and say they "left" the study at times 0, 1, 2, 5, 8 20 and 35 IF they are currently disabled?
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