Stata The Stata listserver
[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

st: Getting Panel Data Ready for Survival Analysis


From   Jason Hwang <jjhwang@fas.harvard.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: Getting Panel Data Ready for Survival Analysis
Date   Wed, 23 Feb 2005 23:46:08 -0500 (EST)

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
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index