Dear Maarten,
thanks a lot for Your (as usual) Kind and helpful hints.
In the meantime, I have performed an acid test on frequencies and values
with tabulate dosea1 and everything was OK (.2 included).
Thanks a lot again for Your Kindness and for Your time.
Cheers,
Carlo
-----Messaggio originale-----
Da: [email protected]
[mailto:[email protected]] Per conto di Maarten Buis
Inviato: venerd� 13 luglio 2007 11.54
A: [email protected]
Oggetto: st: RE: Difference between codebook and count
--- Carlo Lazzaro wrote:
> I have experienced the following problem (please, see details below) with
.2
> value, which is reported with codebook but seemingly ignored with count.
> . codebook dosea1
>
----------------------------------------------------------------------------
> dosea1
> (unlabeled)
>
----------------------------------------------------------------------------
> type: numeric (float)
>
> range: [.2,1] units: .1
<snip>
>
>. count if dosea1==.2
> 0
This is a due to the fact that computers and Stata count in base-2 and we
count
in base-10 numbers. The number .2 (base-10) cannot be held exactly in
base-2.
See the example below, and the possible solution using -round- in the -cond-
statement.
*------------- begin example -------------------
scalar x = .2
di %23.18f x
di "x " cond(x==.2,"is ", "is not ") ".2"
di "round(x,.1) " cond(round(x,.1)==.2,"is ", "is not ") ".2"
*--------------- end example --------------------
(For more on how to use examples I sent to the Statalist, see
http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )
For more on this issue see (Cox 2006) and (Gould 2006).
Hope this helps,
Maarten
N.J. Cox (2006), "Stata tip 33: Sweet sixteen: Hexadecimal
formats and precision problems", The Stata Journal, 6(2),
pp. 282-283.
W. Gould (2006), "Mata Matters: Precision", The Stata Journal, 6(4),
pp. 550-560.
-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands
visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434
+31 20 5986715
http://home.fsw.vu.nl/m.buis/
-----------------------------------------
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