Re: st: RE: counting across individuals within groups

[Buzz Burhans <wsb2@cornell.edu>]

thanks Nick,

I still can't get what I need.  What you suggested gives me a count of all 
the cows on a farm that have entered the pen  cumulative as of the date 
they enter, and unconditioned on whether the other cows that entered the 
pen on a given farm are still present in the pen when a particular cow 
leaves.  Note that farm and pen are different, all cows with the same 
farmid are present on the farm, but only a subset are present in the pen on 
any given date, and the cohort present on the day any given cow exits the 
pen is conditional on the dates the other cows entered and exited.  It is a 
count of that subset cohort that I need, and presence in the cohort may be 
different for each "ExitiingCow" and is conditional on several factors 
relative to each unique "ExitingCow" as follows:

1. farmid is matched with farmid of "ExitingCow"
AND
2. subset cohort cows must have enterPen dates < exitPen dates of the 
particular ExitingCow I am making the count for (i.e. cohort cows entered 
the pen before the ExitingCow left it)
AND
3. subset cohort cows must have exitPen dates > exitPen date of the 
ExitingCow (i.e. cohort cows had to still be present in the pen when 
ExitCow left.

that is, cohort cows have to be on the same farm, enter the pen before 
ExitCow leaves it, and still be there when ExitCow leaves it.

If it helps to make sense of what I am after, I am interested in the 
association of population density in a pen at the day of exit and outcomes 
for cows that are in certain management pens, i.e. maternity or treatment 
pens. I have dates each cow on a farm entered or left the pens in question, 
what I need is to figure out a count of the cohort present at each cows 
exit from the pen.

. list farmid cowid   enterPEN  exitPEN enteredsofar Present if farmid ==3, 
table clean

       farmid   cowid   enterPEN    exitPEN   entere~r 
Count(CowsinPenOnHerExitDate)
 50.        3      19   01/04/02   01/18/02          1          3
 51.        3      18   01/04/02   01/22/02          2          2
 52.        3      20   01/04/02   01/22/02          3          2
 54.        3      22   01/18/02   02/04/02          5          1
 55.        3     581   03/01/02   03/24/02         11         2
 56.        3      25   03/01/02   03/02/02          7
 57.        3      26   03/01/02   03/21/02          9
 58.        3     582   03/01/02   03/22/02         10
 59.        3     579   03/01/02   03/12/02          8
 60.        3     580   03/08/02   04/01/02         12
 61.        3     583   03/27/02   04/03/02         13
 62.        3      13   03/27/02   04/06/02         14

The entere~r is the var that resulted from my test of your code.  The 
"Count" is what I am after.  For example, look at cowid 581.  10 cows 
entered before she exits, but 4 cows that entered before she did exited 
before she exits, so they are not in her cohort at exit. Of the 6 other 
cows that entered before she exited, 4 not only entered, they also exited 
before she did, so they are also not there when she exits.  Only cow 580 
entered before she exited, but had not exited yet, so the cohort at her 
exit is 581 and 580.

Thanks for following my ruminations.

Buzz Burhans
Department of Animal Science
Cornell University


At 04:45 PM 1/30/03 +0000, you wrote:

> Buzz Burhans ruminated
> >
> > I would appreciate help with creating the following value,
> > I can't seem to
> > get it right:
> >
> > I have data with 4 vars in each record as follows:
> >
> > 1. farmID     is an ID variable for farm
> > 2. cowID      is an ID variable for cow (within farmID)
> > 3  enterPen   is the date on which a cow enters Pen
> > 4  exitPen    is the date on which the cow exits Pen
> >
> > There are multiple cows within each farm, and their
> > enterPen and exitPen
> > dates vary individually.
> >
> > What I need is a variable that contains the count of cows
> > within the same
> > farmID which have entered, but not yet exited the Pen on the date an
> > individual cow exits the Pen,
> >
> > i.e.a count of  "other cows" within the same farmID whose
> > enterPen date is
> > < exitPen date for each individual cow (within the same
> > farmID) and whose
> > exitPen date (the "other cows" ) is > the exitPen date for
> > the individual
> > cow ...
> >
> > I can't seem to get the ifs to work correctly across
> > different records,
> > probably because I'm not very good at looping.
> >
>
> There may be a way to approach this with -st-
> but -st- is not my daily bread, so I will
> pass on that and try a direct approach.
>
> I don't think -if- enters here, nor need
> any looping. I surmise that you can get exactly
> what you want with -by-. It's just that I
> don't understand exactly what you want.
>
> Any cow is still within the farm until the
> day it exits. I don't see that -enterPen-
> is relevant so long as -enterPen- <= -exitPen-.
>
> A step towards what you want is, I think,
>
> bysort farmID (exitpen) : gen enteredsofar = _n
> qui by farmID exitpen :
>         replace enteredsofar = enteredsofar[_N]
>
> The number of other cows appears to be central,
> which means subtract 1 from this, I guess.
>
> Nick
> n.j.cox@durham.ac.uk
>
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