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st: Problems with -ipolate-


From   "Jann Ben" <ben.jann@soz.gess.ethz.ch>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Problems with -ipolate-
Date   Mon, 5 Sep 2005 22:49:19 +0200

Hi, 
Stata's -ipolate- command produces results I don't 
understand. Here is an example:

	. set seed 2346
	. sysuse auto
	. drop if rep78<. & uniform()<.8
	. ipolate rep78 mpg, g(rep78i)
	. sort mpg
	. list rep78 mpg rep78i, clean
	
	       rep78   mpg   rep78i
	  1.       .    14        .
	  2.       4    15      3.5
	  3.       3    15      3.5
	  4.       3    16        3
	  5.       2    17      3.5
	  6.       5    17      3.5
	  7.       3    18        3
	  8.       3    19        3
	  9.       3    19        3
	 10.       .    19        3
	 11.       3    21        3
	 12.       .    22      3.5
	 13.       4    23        4
	 14.       4    25        4
	 15.       4    25        4
	 16.       .    26      4.1
	 17.       .    26      4.1
	 18.       5    35        5

-help ipolate- states that rep78i should equal rep78 
if rep78 is not missing ("ipolate creates newvar = yvar, 
where yvar is not missing"). This is certainly not the case 
in the above example. For some reason, "3.5" is stored 
for cases 2, 3, 5, and 6. Can someone explain this to me?

Many thanks,
ben

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