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st: RE: Comparing variables by observation


From   Nick Cox <n.j.cox@durham.ac.uk>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Comparing variables by observation
Date   Tue, 21 Sep 2010 19:57:42 +0100

No code of yours allows no comment on that. 

Responding to the algebra given, this kind of problem is one in which Stata's syntax is inescapably long-winded. To save checking on precedence rules I tend to parenthesise aggressively: 

(5 >= X1) & (X1 >= X2) & (X2 >= X3) & (X3 >= 4) 

(X1 <= 3) & (5 <= X3) 

What you wrote is not illegal but it will be interpreted in terms of 1s and 0s as explained at length in 

http://www.stata.com/support/faqs/data/trueorfalse.html

which will usually yield something quite different from what you want. 

Nick 
n.j.cox@durham.ac.uk 

Anisa Shyti

I have three variables X1 X2 X3
(taking values from 1 to 10) and I need to compare their values, by
observation, according to several conditions (which are theoretically
derived) of the form, examples: (1) 5>= X1 >=X2 >=X3 >=4; (2) X1<=3
and 5<= X3.  I need to evaluate each condition on the data by counting
the number of times it is met, in order to classify the observations.

I tried several approaches, but the total number of classified
observations exceeds the total number of observations.  So, I am
guessing I have some redundant counts - maybe I am doing something
wrong with the coding (given that the conditions are correct).


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