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# st: RE: RE: AW: RE: Re: Generate Variable

 From "Nick Cox" To Subject st: RE: RE: AW: RE: Re: Generate Variable Date Fri, 13 Mar 2009 14:23:44 -0000

```In fact, the -egen- call should go altogether. For example,

gen numProp4 = numProp if wavenum == 4, by(id)
bysort id (numProp4) : replace numProp4 = numProp4

is as much as is to be needed. -egen- was invoked because

egen numProp4 = total(numProp * (wavenum == 4)), by(id)

gets you there in one line whenever there is precisely one non-missing
value for wavenum 4 in each panel -- at the expense of lots of extra
lines off-stage. But once you are realistic about missings, retreating
to a first principles approach becomes a much better strategy.

Nick
n.j.cox@durham.ac.uk

Nick Cox

[Martin] raises a good question about missings. Here's a
better approach if missings are present:

egen numProp4 = mean(numProp) if wavenum == 4, by(id)
bysort id (numProp4) : replace numProp4 = numProp4

egen numInsArrng6 = mean(numInsArrng) if wavenum == 6, by(id)
bysort id (numInsArrng6) : replace numInsArrng6 = numInsArrng6

gen myindicator = numProp4 < numInsArrng6 if !missing(numProp4,
numInsArrng6)

Martin Weiss

Nick Cox

Another approach:

I infer panel structure with an identifier, and at most one measurement
for each -wavenum-. If that is so

egen numProp4 = total((wavenum == 4) * numProp) , by(id)

and

egen numInsArrng6 = total((wavenum == 6) * numInsArrng) , by(id)

spread values in particular wave numbers to all observations with the
same identifier. For example,

wavenum == 4

is 1 if wavenum is 4 and 0 otherwise, so the ensuing total is just the
value of numProp for wavenum == 4.

The required indicator variable follows directly.

Note that even Erick's -if- condition had been correct (it isn't), his
expression for indicator (dummy in his terminology) would have yielded 1
and missing, not 1 and 0.

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