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st: RE: dummy creation


From   "Steichen, Thomas J." <SteichT@rjrt.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: dummy creation
Date   Thu, 6 Oct 2005 08:17:13 -0400

Dirk Nachbar writes:
 
I have a syntax question and help would be appreciated. 
I want to generate a dummy if certain conditions apply, 
but it does not seem to work as the early dummy is always 0. 

gen early=0 
if sex==1 & (anypen1==1 | anypen2==1 | anypen3==1 | anypen4==1 | anypen5==1) & age < 65 { 
early=1 
} 
if sex==2 & (anypen1==1 | anypen2==1 | anypen3==1 | anypen4==1 | anypen5==1) & age < 60 { 
early=1 
} 

---------------------------

The problem is that -if- does not operate value by value.  
Rather it assumes -sex- is shorthand for -sex[1]-, that is, 
the value of the first observation (in current sort order) of sex.

You must use 

  gen early = 0
  replace early = 1 if sex==1 & (anypen1==1 | anypen2==1 | anypen3==1 | anypen4==1 | anypen5==1) & age < 65
  replace early = 1 if sex==2 & (anypen1==1 | anypen2==1 | anypen3==1 | anypen4==1 | anypen5==1) & age < 60 

Or, you can consider using the -cond()- function (See Nick Cox's article in the recent Stata Journal)


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