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Re: st: repeated measures at two time points

From   Ernest Berkhout <>
Subject   Re: st: repeated measures at two time points
Date   Mon, 01 Sep 2003 17:40:04 +0200

At 17:12 1-9-2003, you wrote:
I hope someone can give me some pointers.  I have data on a few individuals
(n=12) and for each person I have two measurements.

The first was made at the last time of exposure (the calendar date differs
for each person)
The second was made on the same calendar date.

So the follow-up differs for each person, (mean (sd) follow-up 89 (108)
months).  So follow-up varies a lot.

I can graph these two-time points for all individuals: with the x-axis being
time since last(final) exposure and the actual measurement value on the
This produces a graph with 12 straight lines all starting at time 0 and
ending at different points.

Now my question is  - how can I summarise these 12 "lines".  I need to get
one curve/line.
What is your null hypothesis? Can't you just plot the _difference_ in measurement value against the _difference_ in days between measurement and follow-up? You get 12 points in which may seem to indicate some relationship between followup-time and measurement-difference. Although significance should be considered carefully with such a small sample, I guess.

Ernest Berkhout
SEO Amsterdam Economics
University of Amsterdam

Room 3.08
Roetersstraat 29
1018 WB Amsterdam
The Netherlands

tel.:+ 31 20 525 1657
fax:+ 31 20 525 1686
A statistician: someone who insists
on being certain about uncertainty

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