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# RE: st: Analysis of event history data

 From Nick Cox <[email protected]> To "'[email protected]'" <[email protected]> Subject RE: st: Analysis of event history data Date Wed, 21 Mar 2012 12:39:46 +0000

```If all times are present and equally spaced, then you can do things like this (a "Yes, of course" trick I learned from Michael Blasnik):

bysort id (time) : gen sumtodate = sum(employment)

by id : gen sumlastyear = sumtodate - sumtodate[_n-52]

For a more general procedure that copes with messier data, see

SJ-7-3  pr0033  . . . . . . . . . . . . . .  Stata tip 51: Events in intervals
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
Q3/07   SJ 7(3):440--443                                 (no commands)
tip for counting or summarizing irregularly spaced
events in intervals

That is accessible at http://www.stata-journal.com/sjpdf.html?articlenum=pr0033

Nick
[email protected]

Kristian Thor Jakobsen

That's so true because I have one more.....

I now have my data sorted in the following way, where the variable status is a dummy indicating if a person has exited from a specific programme during a spell of unemployment. Now I need to calculate the average number of weeks that the person has been employed during e.g. the past two years before exiting this programme (for example, employment[_n-1] to employment[_n-104] if status[_n]==1), but I can't make STATA do the correct calculation (it is taking the mean total employment of each person).

Id      Status  Employment	Time
1       0       1		1
1       1       0		2
1       0       0		3
2       0       1		1
2       0       1		2
2       0       0		3
3       0       0		1
3       0       1		2
3       1       1		3

Any idea of how to get around this?

Really appreciate the help.

Nick Cox

Never say "one final question"!

-help egen- shows that there are -egen- functions -anycount()-, -anymatch()-. -anyvalue()-. So

egen ones = anycount(y_*), values(1)
keep if ones

Even if those functions did not exist, you could do this

gen ones = 0

quietly foreach v of var y_* {
replace ones = ones + (`v' == 1)
}

keep if ones

Nick

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