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help for gen_tail
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Generate an indicator variable, indicating which observations are at or after a
>  given observation.

        gen_tail varname, gen(newvar)


Description

    gen_tail generates an indicator variable (valued 0 or 1), with values of
    1 corresponding to the "tail end" of a series of observations.  The tail
    starts at the first nonzero value (including missing) in varname and
    continues until the end of the dataset or by-group.

    Typically, varname is itself an indicator variable, though any numeric
    variable will suffice.

    by ... : may be used with gen_tail.  Typically, you would use it with by
    and you would include a secondary by-variable or set of by-variables; see
    help by and the example, below.


Example

    . bysort personid (year): gen_tail incm_mis, gen(incm_mis_tail)

    In such a usage, it is the user's responsibility to insure that the
    secondary by-variable(s) (year, in this case), in combination with the
    primary by-variable(s), establish a unique sort order.  Otherwise, you
    will not have meaningful or consistent results.

    A typical usage sequence would be as follows.

    . gen byte incm_mis = mi(income)
    . bysort personid (year): gen_tail incm_mis, gen(incm_mis_tail)
    . logit outcomevar ... income ...  if ~incm_mis_tail


Remarks

    gen_tail was created for use with duration data, though it may be useful
    in other data-construction situations.  With duration data, it is used
    for creating variables that indicate censoring, where censoring begins at
    the first occurrence (within a spell) of a censoring event.  That is, a
    censoring event causes its own observation to be omitted, along with all
    subsequent observations within the spell.


Author

    David Kantor, Institute for Policy Studies, Johns Hopkins University.
    Email dkantor@jhu.edu if you observe any problems.

Also See

    carryforward, a related program by the same author.