I guess what is meant here is
bysort id (time) : gen MOREED2 = sum(MOREED)
Nick
[email protected]
David Bell
> An additional wrinkle, if you conceptualize education as cumulative,
> is to replace
>
> replace MOREED2 = max(MOREED, L.MOREED2)
>
> with
>
> replace MOREED2 = sum(MOREED, L.MOREED2)
n j cox wrote:
> > This calculation is canned as the -egen- function
> > -record()-. A record, recall, is the maximum or
> > minimum seen so far. Here is the whole Kit and
> > caboodle, modulo line wraps:
> >
> > . ssc type _grecord.ado
> > *! 1.2.1 CFB/NJC 8 Oct 2001
> > * 1.2.0 CFB/NJC 8 Oct 2001
> > * 1.1.0 CFB 06 Oct 2001
> > program define _grecord
> > version 6.0
> > syntax newvarname =/exp [if] [in] [, BY(varlist) ORDER
> > (varlist) MIN ]
> > tempvar touse obsno
> > local op = cond("`min'" == "min", "min", "max")
> > quietly {
> > mark `touse' `if' `in'
> > gen `typlist' `varlist' = `exp' if `touse'
> > gen long `obsno' = _n
> > sort `touse' `by' `order' `obsno'
> > by `touse' `by': /*
> > */ replace `varlist' = `op'(`varlist',`varlist'[_n-1]) if
> > `touse'
> > }
> > end
> >
> > In Christer's case, and in others, you don't need the
> > canned version, although it may come in useful.
> >
> > Assuming a -tsset- panel, you can do it with
> >
> > gen MOREED2 = 0
> > replace MOREED2 = max(MOREED, L.MOREED2)
> >
> > Let's see how this works with
> >
> > 1 0
> > 2 0
> > 3 0
> > 4 1
> > 5 1
> > 6 0
> > 7 0
> > 8 0
> > 9 0
> > 10 0
> >
> > First off, using L. means that the -replace-
> > is done within panels.
> >
> > Second, recall that -replace- uses the sort
> > order of the data. In the first obs, the
> > new value is max(MOREED[1], L.MOREED2[1]).
> > There is no obs before the first, so L.MOREED2[1]
> > evaluates to missing, but this problem is no problem
> > as max(non-missing, missing) is always non-missing.
> > So MOREED2[1] is now 0.
> >
> > In the second obs, we get max(0,0) which again
> > is 0.
> >
> > Same story until the fourth obs, in which we
> > get max(1, 0) which is 1. In the next obs
> > we get max(1, 1) which is 1. But
> > in the next we get max(0,1) which is 1.
> >
> > In fact, once the MOREED2 being -replace-d first hits a value of 1
> > it sticks there, which is what was asked for.
> >
> > Note that the initialisation of MOREED2 is arbitrary.
> > We just need it to exist before it can be -replaced-.
> >
> > Or, not quite. More concisely, you can do it with
> >
> > gen MOREED2 = max(L.MOREED2, MOREED)
> >
> > This may well look bizarre to you, as the RHS refers
> > to a variable that doesn't yet exist, but I have it
> > on good authority that in this case this metaphysical-
> > theological difficulty "non tenet aquam", as Aquinas
> > probably said.
> >
> > At least, this works in Stata 8, which is what
> > I have access to right now.
> >
> > Nick
> > [email protected]
> >
> >
> > Christer Thrane
> >
> > In my yearly panel data I follow a number of college
> undergraduates
> > for
> > about ten years after they graduate. Each year after graduation
> > their yearly earnings are recorded along with a binary variable
> > (called MOREED) that indicates whether or not they were
> enrolled in
> > "above-undergraduate" education in that year (1 = yes, 0 = no).
> > Thus, if a person during the time period first works full-time for
> > three years after graduation before going to the university
> for two
> > more years and then return to working full-time, he or she will
> > have the following panel sequence for the variable MOREED:
> >
> > 0 (year 1), 0 (year 2), 0 (year 3), 1 (year 4) 1 (year 5),
> 0, 0, 0,
> > 0, and 0
> > (year 6, 7, 8, 9, and 10).
> >
> > When I, using -xtreg, re-, model log earnings as function
> of MOREED
> > and
> > controls, the former coefficient is large, negative and
> > significant. I guess this makes sense--in the same year as
> a person
> > goes to school, he or she does not have (enough) time to work full-
> > time.
> >
> > On the other hand, common sense suggests that increasing ones
> > knowledge (by taking up more education) should "pay off" in the
> > longer run. In other words, MOREED should be positive. In this
> > respect, I'm wondering if maybe the problem is the coding of the
> > variable MOREED. From year 5 to 6, this variable changes its value
> > back from 1 to 0. And although this "makes sense" in the data, it
> > does, in my opinion, not make sense in reality--you cannot "go
> > back" from, say, being a graduate to being an undergraduate. My
> > question therefore becomes:
> >
> > How can I change the variable MOREED so that it keeps the value of
> > 1 in the remaining panels after it gets a 1 for the first time.
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