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Re: st: Analysing longitudinal data
From
Nick Cox <[email protected]>
To
[email protected]
Subject
Re: st: Analysing longitudinal data
Date
Tue, 26 Feb 2013 15:39:33 +0000
I don't think any programming is needed here at all, just a few
commands issued in a do-file or interactively.
Your first two questions are of the form
{count|average} in moving time interval
and both are addressed in moderate detail within
SJ-7-3 pr0033 . . . . . . . . . . . . . . Stata tip 51: Events in intervals
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox
Q3/07 SJ 7(3):440--443 (no commands)
tip for counting or summarizing irregularly spaced
events in intervals
http://www.stata-journal.com/sjpdf.html?articlenum=pr0033
The last has been discussed in various places, but rather than
references here is some sample code.
gen NotWanted = (value < 1) | missing(value)
bysort ID (NotWanted Date) : gen TimeSinceLast = Date - Date[_n-1] if
!NotWanted
The logic looks a little contrived, but the idea is to get a sort
order that looks like this, so that the time since the
last previous event is just the current date minus the previous date.
For individual, there will be only one such date,
30/04/2011, for which the answer will be 2 days. The answer for the
first will be missing.
1 1.5 28/04/2011
1 1.3 30/04/2011
1 0.6 02/03/2010
1 0.6 24/05/2010
1 0.6 16/08/2010
1 0.6 10/11/2010
1 0.9 09/02/2011
1 0.7 01/05/2011
1 0.6 03/05/2011
1 0.6 09/05/2011
Once you have values in a variable, -summarize- gives you the mean.
Nick
On Tue, Feb 26, 2013 at 3:18 PM, K Jensen <[email protected]> wrote:
> I have a dataset that looks like the sample I have pasted in at the
> end of this message, with repeated measures over time on the same
> individuals.
>
> I would like to answer questions like:
> When a value was over 1, how many were measured again within the next
> week? How many of those were also over 1?
> What was the average interval between a value being over 1 and the
> next value for that individual?
>
> How would I go about programming this in Stata?
>
> Thankyou
>
> Karin
>
> ID Value Date
> 1 0.6 02/03/2010
> 1 0.6 24/05/2010
> 1 0.6 16/08/2010
> 1 0.6 10/11/2010
> 1 0.9 09/02/2011
> 1 0.7 01/05/2011
> 1 1.5 28/04/2011
> 1 1.3 30/04/2011
> 1 0.6 03/05/2011
> 1 0.6 09/05/2011
> 2 0.6 14/04/2009
> 2 0.7 23/07/2009
> 2 0.6 16/11/2009
> 2 0.6 29/12/2009
> 2 0.6 30/03/2010
> 2 0.9 01/07/2010
> 2 1.2 27/09/2010
> 2 0.7 12/10/2010
> 2 0.7 26/10/2010
> 2 0.8 25/03/2011
> 3 0.3 21/01/2009
> 3 0.3 05/11/2009
> 3 0.1 01/03/2010
> 3 0.2 24/05/2010
> 3 0.2 18/08/2010
> 4 0.9 16/02/2010
> 4 1.0 01/03/2010
> 4 0.9 12/03/2010
> 4 1.1 25/03/2010
> 4 0.5 01/06/2010
> 4 0.4 31/08/2010
> 4 0.6 30/11/2010
> 4 0.6 19/04/2011
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