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Re: st: Getting Panel Data Ready for Survival Analysis


From   Ichiro Fujikake <fujikake@cc.miyazaki-u.ac.jp>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Getting Panel Data Ready for Survival Analysis
Date   Thu, 24 Feb 2005 16:29:05 +0900

Hi Jason,

How about

drop if quantity==0
bysort sid pid bid (year): keep if _n==1

for (1), and,

bysort sid pid year (quantity) : keep if _n==1
gen answer=year if quantity>=50
bysort sid pid (answer): keep if _n==1

for (2)?
For (1) you can change the order of the two commands. But I suppose
restricting sample first is faster (but insignificantly maybe).

Ichiro


On 05.2.24 13:46, "Jason Hwang" <jjhwang@fas.harvard.edu> wrote:

> Dear Statalist Users,
> 
> I have panel data and I would like to extract certain information for a
> survival analysis. Conceptually, I have data on supplier, buyer and
> quantity sold and I want to ask: when is the first date at which buyer
> buys more than x amount.
> 
> My data is of the following form:
> 
> year sid pid bid  quantity
> 1990 111 1   555  0
> 1990 111 1   777  10
> 1990 111 2   555  100
> 1990 111 2   777  0
> 1991 111 1   555  3
> 1991 111 1   777  25
> 1991 111 2   555  5
> 1991 111 2   777  5
> 
> sid: seller id
> pid: product id
> bid: buyer id
> 
> So this tells me for each seller, how much product they sold to which
> buyer. Now I want to ask two questions:
> 
> (1) For each seller and for each product and buyer, when is the first year
> at which quantity sold is positive?
> 
> So the output I would want would be:
> 
> sid pid bid answer
> 111 1   555 1991
> 111 1   777 1990
> 111 2   555 1990
> 111 2   777 1991
> 
> The complication is that in the real data, quantity sold may become
> positive, zero, then again positive. How can I only pick up the first time
> it becomes positive?
> 
> With this simple data, it's relative easy. I can just sort by sid pid bid
> and pick the first year that comes up but I was wondering if there's a
> more elegant way that's also quicker.
> 
> (2) This is trickier. For each selle and product, I want the first year at
> which quantity sold is at least x for all buyers. For example, say x=50.
> mThen my answer would be
> 
> sid pid answer
> 111 1  .
> 111 2  .
> 
> since in neither year does the seller sell more than 50 to ALL buyers.
> 
> However if x=5, then the output woud be
> 
> sid pid answer
> 111 1  .
> 111 2  1991
> 
> I would appreciate any hints. Any references or tricks for getting this
> type of panel data ready for survival-type analysis would be helpful as
> well. Thank you very much for your help.
> 
> Jason Hwang
> *
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> 


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