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Re: st: elapsed time between incidents


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: elapsed time between incidents
Date   Tue, 19 Feb 2013 23:19:38 +0000

I don't think anyone can be expected to choose the same words as me,
so searching for this inevitably seems difficult.

Nick

On Tue, Feb 19, 2013 at 9:34 PM, Steven Archambault
<archstevej@gmail.com> wrote:
> Okay, thanks for this. I apologize for not finding the tip prior to
> posting. My chosen search words were off!
>
> On Tue, Feb 19, 2013 at 2:08 PM, Nick Cox <njcoxstata@gmail.com> wrote:
>> This kind of problem was discussed in my posts
>>
>> http://www.stata.com/statalist/archive/2011-01/msg00999.html
>>
>> http://www.stata.com/statalist/archive/2012-08/msg00633.html
>>
>> and in a Tip
>>
>> Cox, N.J. 2011. Stata tip 101: Previous but different. Stata Journal
>> 11(3): 472-473.
>>
>> No doubt there are other references.
>>
>> Here's some code:
>>
>> . clear
>>
>> . input id day incident
>>
>>             id        day   incident
>>   1.  1  1      6
>>   2.  1   2     .
>>   3.  1   3     .
>>   4.  1  4      .
>>   5.  1   5     8
>>   6.  1   6     .
>>   7.  1   7     5
>>   8. end
>>
>> . bysort id (day): gen prev = day[_n-1] if incident[_n-1] < .
>> (5 missing values generated)
>>
>> . by id: replace prev = prev[_n-1] if missing(prev)
>> (4 real changes made)
>>
>> . gen elapsed = day - prev if incident < .
>> (5 missing values generated)
>>
>> . l, sep(0)
>>
>>      +--------------------------------------+
>>      | id   day   incident   prev   elapsed |
>>      |--------------------------------------|
>>   1. |  1     1          6      .         . |
>>   2. |  1     2          .      1         . |
>>   3. |  1     3          .      1         . |
>>   4. |  1     4          .      1         . |
>>   5. |  1     5          8      1         4 |
>>   6. |  1     6          .      5         . |
>>   7. |  1     7          5      5         2 |
>>      +--------------------------------------+
>>
>> The nub of the matter is that the previous event can be picked up in
>> the following observation for the same identifier. After that we just
>> copy down as required in a cascade.
>>
>> FAQ     . . . . . . . . . . . . . . . . . . . . . . . Replacing missing values
>>         . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
>>         2/03    How can I replace missing values with previous or
>>                 following nonmissing values?
>>                 http://www.stata.com/support/faqs/data/missing.html
>>
>> -by:- makes doing this by panels no more difficult than doing it if
>> there were no panels.
>>
>> Steve said non-zero, but his example implies non-missing; whatever the
>> exact condition is can no doubt be substituted easily.
>>
>> Nick
>>
>> On Tue, Feb 19, 2013 at 8:45 PM, Steven Archambault
>> <archstevej@gmail.com> wrote:
>>
>>> I have unbalanced panel data where an incident (measured by a non-zero
>>> value) occurs randomly in the panel. I want to calculate the time
>>> (days_elapsed) between incidents. Here is an example:
>>>
>>> id day incident days_elapsed
>>> 1  1      6             .
>>> 1   2     .              .
>>> 1   3     .              .
>>> 1  4      .              .
>>> 1   5     8             4
>>> 1   6     .              .
>>> 1   7     5             2
>>>
>>> Thanks for any help here.  I have not been able to find this.
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