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st: RE: Ignore dummy variable in predict function?

From   "Martin Weiss" <>
To   <>
Subject   st: RE: Ignore dummy variable in predict function?
Date   Mon, 9 Nov 2009 23:56:42 +0100


sysuse uslifeexp.dta, clear

gen le_measure1=le
replace le_measure1=le-5 if year<=1950 | inlist(year, 1965, 1972, 1986,

gen byte measuredummy=!(le_measure1==le)

regress le_measure1 year measuredummy

//hibernate the dummy for later...
tempvar temp
clonevar `temp'=measuredummy

replace measuredummy=0
predict predat0
replace measuredummy=1
predict predat1
// and back to original state..
replace measuredummy= `temp'


-----Original Message-----
[] On Behalf Of Dorothy Bridges
Sent: Montag, 9. November 2009 23:28
Subject: st: Ignore dummy variable in predict function?

Dear Statalist:

I have a dataset in which my dependent variable -- say, life
expectancy, so I can use the uslifexp.dta file as an example -- is
measured according to two different methods.  In other words, life
expectancy is measured according to method a in some years and method
b in other years.  Method a always yields measures that are lower than
those generated with method b, though much lower varies by

I would like to identify the time trend in this data.  Hence I regress
the outcome variable on year and a dummy variable for the observations
generated with method a, a la:

sysuse uslifeexp.dta, clear

**(Imitating my actual data)
gen le_measure1=.
replace le_measure1=le-5 if year<=1950 | year==1965 | year==1972 |
year==1986 | year==1989
replace le_measure1=le if le_measure1==.

**The regression:
gen measuredummy=1
replace measuredummy=0 if le_measure1==le

regress le_measure1 year measuredummy

Now I would like to generate predicted values of le, **as if** all of
the method-a observations had been created using method b.  In other
words: when I follow the regress command with "predict le_predict" and
then look at "twoway (scatter le_measure1 year) (lfit le_measure1
year) (line le_predict year)", I want the le_predict line (green) to
be straight.  It would be something like "predict le_predict as if
measuredummy==0," if such a command existed.

Thank you!!

D. Bridges
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