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Re: st: AW: Diffrence between sum and tabsum


From   Ulrich Kohler <kohler@wzb.eu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: AW: Diffrence between sum and tabsum
Date   Tue, 15 Sep 2009 13:41:33 +0200

To follow up

. set obs 3
. gen byte coreweight1968=18
. gen float firstweight =   coreweight1968 *  60468000/78028
     ^^^^^
. gen dummy = 1
. tab dummy, sum(firstweight)

works nicely. Seems like -tabulate, summarize- internally creates a
float to store something. 


Uli

Am Dienstag, den 15.09.2009, 13:32 +0200 schrieb Ulrich Kohler:
> <>
> 
> yes, I thought about that. However, the following bit shows that your
> example is not quite the problem here
> 
> . set obs 3
> . gen byte coreweight1968=18
> . gen double firstweight =   coreweight1968 *  60468000/78028
> . format firstweight %32.20f
> . l
> 
>      +-----------------------------------------------+
>      | cor~1968                  firstweight   dummy |
>      |-----------------------------------------------|
>   1. |       18   13949.14646024503963417374       1 |
>   2. |       18   13949.14646024503963417374       1 |
>   3. |       18   13949.14646024503963417374       1 |
>      +-----------------------------------------------+
> 
> . gen dummy = 1
> . tab dummy, sum(firstweight)
> 
>             |       Summary of firstweight
>       dummy |        Mean   Std. Dev.       Freq.
> ------------+------------------------------------
>           1 |   13949.146   .00024815           3
> ------------+------------------------------------
>       Total |   13949.146   .00024815           3
> 
> 
> However you are right that is should be some kind of a precision
> problem. In fact 
> 
> . replace firstweight =   coreweight1968 *  4/3
> . tab dummy, sum(firstweight)
> 
> works as expected.
> 
> 
> Am Dienstag, den 15.09.2009, 12:54 +0200 schrieb Martin Weiss:
> > <> 
> > 
> > 
> > Probably a precision issue as in
> > 
> > ***
> > 
> > clear*
> > 
> > inp double firstweight
> > 13949.1460454864
> > 13949.146248765 
> > 13949.146324324
> > end
> > 
> > 
> > gen byte dummy=1
> > 
> > su firstweight
> > 
> > tab dummy,  /* 
> > */ sum(firstweight)
> > 
> > ***
> > 
> > 
> > 
> > HTH
> > Martin
> > 
> > -----Ursprüngliche Nachricht-----
> > Von: owner-statalist@hsphsun2.harvard.edu
> > [mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Ulrich Kohler
> > Gesendet: Dienstag, 15. September 2009 12:14
> > An: statalist
> > Betreff: st: Diffrence between sum and tabsum
> > 
> > <>
> > 
> > Does anybody know why -tabulate, summarize- displays a nonzero
> > standard-deviation for a variable that is a constant? 
> > 
> > . tab seopsu if seopsu==948, sum(firstweight)
> > 
> >      Cps Pr |
> >    Sampl Un |       Summary of firstweight
> >     5:71-73 |        Mean   Std. Dev.       Freq.
> > ------------+------------------------------------
> >         948 |   13949.146   .00024815           3
> > ------------+------------------------------------
> >       Total |   13949.146   .00024815           3
> > 
> > . sum firstweight if seopsu==948
> > 
> >     Variable |       Obs        Mean    Std. Dev.       Min        Max
> > -------------+--------------------------------------------------------
> >  firstweight |         3    13949.15           0   13949.15   13949.15
> > 
> > . return list
> > 
> > scalars:
> >                   r(N) =  3
> >               r(sum_w) =  3
> >                r(mean) =  13949.14646024504
> >                 r(Var) =  0
> >                  r(sd) =  0
> >                 r(min) =  13949.14646024504
> >                 r(max) =  13949.14646024504
> >                 r(sum) =  41847.43938073512
> > 
> > . d firstweight 
> > 
> >               storage  display     value
> > variable name   type   format      label      variable label
> > ----------------------------------------------------------------------------
> > ------
> > firstweight     double %10.0g                 
> > 
> > . l firstweight if seopsu==948
> > 
> >       +-----------+
> >       | firstwe~t |
> >       |-----------|
> > 4256. | 13949.146 |
> > 4365. | 13949.146 |
> > 4537. | 13949.146 |
> >       +-----------+
> > 
> > . about
> > 
> > Stata/MP 11.0 for Unix (Linux 64-bit x86-64)
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