confidence intervals

[Kevin Horton-5]

Hi,

I'm trying to do 2 things in SPSS (version 13.0) but am having problems.
Any guidance would be much appreciated.

1. generating 95% confidence intervals for geometric means, and
2. generating 95% confidence intervals for percentiles (i.e. 95th
percentiles).

Thx.

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[Marta Garcia-Granero]

Hi Kevin.

A partial answer:

> I'm trying to do 2 things in SPSS (version 13.0) but am having problems.
> Any guidance would be much appreciated.
>
> 1. generating 95% confidence intervals for geometric means, and
>

This one is easy. Log transform your variable, compute a 95%CI for the
arithmetic mean (part of the output of EXAMINE procedure) and anti-log
the lower and upper limits.

> 2. generating 95% confidence intervals for percentiles (i.e. 95th
> percentiles).
>
That one is going to be harder. Let me Google a bit to find the formula,
and I think some MATRIX code will do the trick.


Regards,
Marta García-Granero

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[Marta Garcia-Granero]

Hi Kevin
> I'm trying to do 2 things in SPSS (version 13.0) but am having problems.
> Any guidance would be much appreciated.
>
> 1. generating 95% confidence intervals for geometric means, and
> 2. generating 95% confidence intervals for percentiles (i.e. 95th
> percentiles).
>

OK, some approaches for question #2:

- See the method implemented here:
http://www2.napier.ac.uk/depts/fhls/peas/percentiles.htm
- Bootstrapping. take a look here
.http://www.spsstools.net/SampleSyntax.htm#Bootstrap

HTH,
Marta

> Thx.
>
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>

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