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Re: st: Difference in values within the same variable
From
Nick Cox <[email protected]>
To
[email protected]
Subject
Re: st: Difference in values within the same variable
Date
Tue, 3 Jan 2012 14:33:19 +0000
This won't work without extra care. Prescription dates occur
irregularly, so any -tsset- or -xtset- would need to be done using a
specially created sequence variable that took successive integer
values for any patient. I concur with Kit Baum in recommending working
with [_n] and [_n-1] rather than time series operators.
Nick
On Tue, Jan 3, 2012 at 2:11 PM, A Loumiotis <[email protected]> wrote:
> Hi Sara,
> You can use:
>
> gen passtime = presc_date - l.presc_date
>
> assuming your dataset is already declared as panel using -xtset- or -tsset-.
>
> Type "help tsvarlist" for help on time series operators.
>
> Antonis
>
> On Tue, Jan 3, 2012 at 3:19 PM, Sara Muller <[email protected]> wrote:
>> Hi,
>>
>> I'm sorry if this is a silly question. I have searched in the help and
>> online, but I don't know what to look up.
>>
>> I have long data with multiple prescriptions per person. I want to define
>> the length of time between successive prescriptions (see data below, which
>> is sorted by patid (person ID) and presc_date (date of prescription)), with
>> the eventual aim of including in my analysis only people who received 2 or
>> more prescription within 6 months of each other.
>>
>> I'm not bothered really how I do this, although I have been trying to do it
>> by calculating another variable that gives the time from the previous
>> prescription (within patid). I believe the equivalent command in SPSS is
>> called a 'lag', but searching for this in Stata doesn't see to have turned
>> up the right stuff.
>>
>> If anyone could point me in the right direction, I'd be very grateful.
>>
>> Best wishes,
>> Sara
>>
>> patid presc_date
>> 4457 11aug1997
>> 4457 18aug1997
>> 4457 15sep1997
>> 4457 29sep1997
>> 4457 27oct1997
>> 4457 15dec1997
>> 4457 15dec1997
>> 4457 16apr1998
>> 4457 11may1998
>>
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