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September 2015 Q7.

A

Aditya mohan mathur

Member
Hi
Can anyone explain me, please, how the hazard in this question is taken to be the event of passing the test?

As per my thinking, since the survival function is of attending the course, the hazard should be the opposite, ie. Dropping out.

Also in Q6, April 2015, I am unable to understand how the hazard taken is of completing the purchase
 
The question isn't really that clear here. However, the last part of the question suggests that what we are interested in is how good the school is at getting students through the exam. So passing the exam is the decrement of interest and students who drop out are considered to be censored.

As always, it's worth a look at the comments in the Examiners Report. Here we're told:

"A minority of candidates supposed that the decrement was dropping out rather than passing the test. As the wording of the question did not rule out this interpretation, full marks were awarded for the correct survival function for this alternative decrement."

April 2015, Q6 appears to have nothing to do with the hazard of completing a purchase. It looks like the wrong reference.
 
Thank you for the reply.

April 2016, Q6 is taking the decrement as completing the purchase.
The examiners comment says that partial credit was given if the event of leaving without purchase was treated as the decrement and followed correctly thereafter.

My thinking goes like,
The survival function is mentioned as duration between joining the queue and completing a purchase.
Therefore, the decrement should be opposite, ie. Leaving without making purchase.

Why is this incorrect is what I am not getting.
Please help with this.
 
We're asked for the "survival function of the duration between joining the queue and completing the purchase". This is telling you that it is completing the purchase that you're interested in, ie this is the decrement of interest. Leaving without making a purchase is censoring.

The decrement occurs when someone leaves the population due to the reason under study.
 
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