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Re: st: Analysing longitudinal data
From
K Jensen <[email protected]>
To
[email protected]
Subject
Re: st: Analysing longitudinal data
Date
Tue, 26 Feb 2013 16:12:01 +0000
Thanks Nick. As ever that is very helpful.
Kind regards
Karin
On 26 February 2013 15:39, Nick Cox <[email protected]> wrote:
> 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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