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Re: st: Identifying visits with 1 time period of an event
From
Nick Cox <[email protected]>
To
"[email protected]" <[email protected]>
Subject
Re: st: Identifying visits with 1 time period of an event
Date
Tue, 18 Feb 2014 00:29:31 +0000
Indicator variables follow from e.g.
(time2 == time) & (time2 - time1) <= 1
Subscript technique also leads to
bysort id (time) : gen within1 = procedure[_n-1] & (followup==1) &
((time - time[_n-1]) <= 1)
The technique I showed earlier appears to have many applications and
is not limited to comparison with the immediately previous
observation.
Nick
[email protected]
On 17 February 2014 23:33, Nick Cox <[email protected]> wrote:
> The first time when something happened is one and the same as the
> minimum time. For panel data, -egen-'s -min()- function serves fine to
> identify such times separately by panels.
>
> Here "something" means either -procedure == 1- or -followup == 1- so
> specifying either condition can be done by instructing Stata to ignore
> anything else. -min()- takes expressions, so that can be made explicit
>
> egen time1 = min( cond(procedure == 1, time, .) ) , by(id)
> egen time2 = min( cond(followup == 1, time, .) ), by(id)
>
> This is equivalent and according to taste cunning or cryptic:
>
> egen time1 = min(time/procedure), by(id)
> egen time2 = min(time/(followup == 1)), by(id)
>
> Now we are on the home straight and contemplating reward:
>
> gen lag = time2 - time1
>
> gen within1 = (time2 - time1) <= 1
>
> For a self-indulgent exploration of similar trickery, see
>
> http://www.stata-journal.com/article.html?article=dm0055
>
> More concise statements are likely to be possible, but may defy
> simultaneous maintenance of sanity and balancing of parentheses.
>
> Nick
> [email protected]
>
> On 17 February 2014 20:23, Paul O'Brien <[email protected]> wrote:
>
>> I have longitudinal data on visits to a clinic during which a procedure sometimes occurs.
>>
>> I want to mark follow-up visits if the procedure occurred and mark the visits within 1 time period of the procedure, as in the last two variables here.
>>
>> clear
>> input ///
>> id time procedure followup followup1
>> 1 1 0 0 0
>> 1 2 1 0 0
>> 1 3 0 1 1
>> 1 4 0 2 0
>> 1 5 0 3 0
>> 2 3 1 0 0
>> 2 4 0 1 1
>> 2 5 0 2 0
>> 2 7 0 3 0
>> 2 8 0 4 0
>> 2 10 0 5 0
>> 3 1 0 0 0
>> 3 2 0 0 0
>> 3 3 0 0 0
>> 3 4 0 0 0
>> 4 2 0 0 0
>> 4 3 1 0 0
>> 4 6 0 1 0
>> 4 7 0 2 0
>> end
>>
>> I have struggled with _n and _N but cannot get the follow to start after the event.
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