Re: st: missing values

[Richard Williams <Richard.A.Williams.5@ND.edu>]

At 01:11 AM 9/22/2005, you wrote:
> Here are my exact commands.
>
> replace sswlnw_1 = .a if (yob > 1912 & a_age > 69)
> replace sswlol_1 = .a if (yob > 1912 & a_age > 69)
> replace sswlnw_2 = .a if (yob > 1912 & a_age > 69)
> replace sswlol_2 = .a if (yob > 1912 & a_age > 69)
>
> If I use . instead of .a, 0 changes are made. (With .a, 57981 changes re made)
>
> If I say gen dummy = 0
> replace dummy = 1 if (yob > 1912 & a_age > 69)
> then 57891 changes are made...
Incidentally, here is a pseudo-cloning of what you are doing (I think):

. sysuse auto, clear
(1978 Automobile Data)

. gen dummy = 0

. replace dummy = 1 if (mpg > 20 & trunk > 15)
(6 real changes made)

. replace price = . if (mpg > 20 & trunk > 15)
(6 real changes made, 6 to missing)

. sysuse auto, clear
(1978 Automobile Data)

. replace price = .a if (mpg > 20 & trunk > 15)
(6 real changes made, 6 to missing)

As you see, it seems to work fine, regardless of whether I use . or .a.

One other Q: What version of Stata are you using?  Is it up to 
date?  I remember there was some problem with Stata a while back 
where it was behaving in odd ways with MD, but then an update fixed 
it.  I don't know if that might apply here or not.


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Richard Williams, Notre Dame Dept of Sociology
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