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List:       sas-l
Subject:    Re: PLEASE HELP
From:       David L Cassell <davidlcassell () MSN ! COM>
Date:       2006-04-24 0:59:49
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fberenice@GMAIL.COM wrote:
>Hi,
>
>I have a couple of questions that I really need to answer...
>
>I need to know what are the basics for longitudinal data analysis and
>for time series.
>
>What are the differences between these two techniques?
>
>When is it convenient to use one or the other?
>
>Please I need to have a clue about this!!
>
>Thanks a lot

First off, writing the same questions over again does *not* make me come
back from vacation any faster.  Please be patient.  The people who answer
questions here have real lives.

Second, your subject line is likely to end up in a lot of trash cans.  Spam
filters are not going to like a subject line like "PLEAE HELP" in all caps,
and
many people are not going to take the time to read your message if you
do not stop and help them with an informative subject line.  A simple
"longitudinal data analysis vs time series" would have told any reader what
you wanted to ask about.

Next, you need to get a book or two to cover the breadth of material
that these areas can hit.  As a general rule, I would say that if you have
hundreds of different time points, then you should probably look at time
series analysis.  If you have half a dozen different time points, then you
should probably look at longitudinal analysis.  If you have 40 different
time points, then you may be able to use *both* analysis approaches.

But a lot of the decisions here depend on your data.  On your data
sources.  On your meta-data.  On the quality of your data.  So, as
Mike sagely pointed out, you need to help us help you.

David
--
David L. Cassell
mathematical statistician
Design Pathways
3115 NW Norwood Pl.
Corvallis OR 97330

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