Re: st: Survey data: how to assign mother's age to child?

 From wgould@stata.com (William Gould, Stata) To statalist@hsphsun2.harvard.edu Subject Re: st: Survey data: how to assign mother's age to child? Date Thu, 08 Jun 2006 13:45:07 -0500

```Friedrich Huebler <huebler@rocketmail.com> has the following data:

hh   id   sex   age   mid   fid
---------------------------------
1     1     1    30     .     .
1     2     2    30     .     .
1     3     1     5     2     1
2     1     1    30     .     .
2     3     2     5     2     1

In this data, mid id the id-within-hh of the mother.

Friedrich wants to add new variable mage, the age of the mother, so that
we would have

hh   id   sex   age   mid   fid   mage
----------------------------------------
1     1     1    30     .     .     .
1     2     2    30     .     .     .
1     3     1     5     2     1    30
2     1     1    30     .     .     .
2     3     2     5     2     1     .   <- mage=. because id=2
does not exist

The solution is to create a dataset containing hh, id, and age, and
then to merge to obtain mother's age.

Call the original data master.dta.

First, I verify something Friedrich has implied:

. use master, clear
. assert hh!=.
. assert pid!=.
. sort hh pid
. by hh pid: assert _n==1

That out of the way, I create the data that I will use to merge.
In this dataset, everybody is a potential mother:

. use master, clear
. keep hh id age
. rename id mid
. rename age mage
. sort hh mid
. save tomerge, replace

Now I merge the original dataset with the data I just created.  I merge on hh
and mid, and I keep only the original observations.  Note that this is a
potentially a many-one merge, because more than one child in a household
can have the same mother.  There's nothing special I need to do, however.

. use master, clear
. sort hh mid
. merge hh mid using tomerge, nokeep
. drop _merge
. sort hh id              // put data back in original order

I'm done, except to clean up,

. erase tomerge.dta

-- Bill
wgould@stata.com
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