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st: using max and sdev functions more flexibly


From   "Pezzini,S (pgr)" <S.Pezzini@lse.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: using max and sdev functions more flexibly
Date   Mon, 4 Nov 2002 14:48:30 -0000

Dear Stata-listers, 

as my programming skills are very low, I would like to ask if someone could help me get around a problem that I've been trying to solve without success.

The starting point is a dataset with inflation for years from 1900 to 1995 and some country codes.
I would like to use the max and sdev function in order to compute the maximum and the standard deviation of inflation over an interval from 1920 (and successive decades) to every year between 1975 and 1995, by country. 
If I type:

by ccode: egen maxinf=max(inflation) if year>=1920

this only allows me to compute max and sdev over 1920 and 1995, i.e. I get a constant over the whole time interval, not staggered by year. I can't get to incorporate the information "compute the standard deviation or the max UP TO EACH YEAR IN THE INTERVAL [1975; 1995]". 

Maybe my request will be clearer if I tell you that I was able to get what I wanted with another function, sum. 
By typing:
by ccode: gen cuminf=sum(abs(inflation)) if year>=1920
I was able to compute the cumulative inflation from 1920 up to each year in the interval [1975; 1995]. This was possible because "gen y=sum(x)", computes a sum where the j-th obs on y contains the sum of the first through j-th observations on x. 

Finally, I am using Stata 7.0 SE in Windows environment.

Maybe this is a straightforward problem for you, so I would be very grateful if you could point me to a solution.

Thanks a lot, 

Silvia Pezzini






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