(This is second time round with this
problem, mostly likely through some
oversight or list malfunction. I
suggest the diagnosis is clear,
so let's close the thread, please.)
Nick
[email protected]
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of
> Ulrich Kohler
> Sent: 17 January 2005 14:44
> To: [email protected]
> Subject: Re: st: A strange data problem
>
>
> Maoyong Fan wrote:
> > I met a strange problem in dealing with my scanner
> data. I use stata
> > transfer to transger the original data to dta files. One
> of my variables
> > is UPC whose storage type is double. I found that when I
> generate a new
> > variable equal to UPC, the new variable is totally
> different from UPC.
> >
> > Like this:
> > gen UPC1 = UPC
> > gen diff = UPC1 - UPC
> > sum
> > des
> >
> > Variable | Obs Mean Std. Dev. Min
> Max
> >
> -------------+--------------------------------------------------------
> > UPC | 1780770 3.76e+10 1.96e+11 1.00e+10
> 2.72e+12
> > UPC1 | 1780770 3.76e+10 1.96e+11 1.00e+10
> 2.72e+12
> > diff | 1780770 144.9445 4290.722 -105114
> 116086
> >
>
> The default Storage type for new variables in Stata is float.
> Float variables
> have about 7 digits of accuracy; If the values in UPC have
> more than 7
> digits, these values have to be rounded to store them in a
> float variable.
>
> To get an exact copy of your variable you need to generate
> UPC1 with double
> precision:
>
> . gen double UPC1 = UPC
>
> Note however, that the difference between 1.000.000.000 and
> 1.000.000.144 is
> probably not very important. Equally one is seldom interested in the
> difference between numbers like 0,1234567144 and 0,1234567000.
>
> More on that can be found under the heading "Precision of
> numeric storage
> types" in help datatypes and in [U] 16.10
>
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