Q&a 5.10

[Sharon]

Hi

Can anyone explain this question to me please? I noticed the earlier thread about this question but I'm still confused.

Mainly I don't understand why we don't include lives 1 and 2 at time 0, who are over 65, but we do include the other 6 lives who aren't yet 65. When lives 3-8 turn 65 I would expect them to join the investigation, not the other way around.

Are we defining time 0 as being 1st January 2001? ie at the start of the investigation?

Thanks

 

[*Ted*]

Have you had a look at the corrected solution in the Corrections document?

Here's the link:

http://www.acted.co.uk/Html/paper_corrections.htm

*Ted*

 

[Sharon]

Hi *Ted*

Yes I had seen that thanks, and the earlier thread in the forum about this question, but I'm still stumped!

 

[Mark Mitchell]

You're measuring time from age 65. This is because we are interested in how long lives survive from age 65 (not how long they survive after 1/1/01).

So you must take the data and order it all based on how long the event happened after age 65 for each life. Hence the statement in the solution that duration is the duration since the 65th birthday. We must also take into account that some lives were over age 65 when they started to be observed (i.e. at the start of the investigation) and that some lives were still alive when they stopped being observed (i.e. at the end of the observation).

So, for instance, life 3 attained age 65 during the period of the investigation, and so is under observation from age 65 (time 0) onwards. This life ceases to be observed at the end of the investigation (duration 5y11m), so we have a -1 in our table to show that they left the investigation at that age.

Life 2 is over age 65 at the start of the investigation, so we do not start to observe them until age 65y5m. They therefore come into our calculations as an increment (addition of 1 life) after 5 months (we're measuring time since the 65th birthday of each individual). This life ceases to be observed at the end of the investigation (duration 6y5m - since they are 6y5m beyond their 65th birthday), so we have a -1 in our table to show that they left the investigation at that age.

Hope this clears it up.

Mark

 

[Sharon]

That makes sense now, thanks a lot.

Another question I hope you can help with - a few of the recommended questions in the old 103 and 104 papers are about pseudo random values. I think this is in CT6 now, so is this likely to come up in CT4?

 

[Mark Mitchell]

Glad to be of service.

No - you shouldn't see these pseudo-random number questions on CT4 (due to the change in syllabus).

Mark.