st: re: finding the longest spell in a _set_ of variables for each panel unit

[Kit Baum <baum@bc.edu>]

 'ONESPELL': module to generate single longest spell for each unit in 
panel data, listwise

DESCRIPTION/AUTHOR(S)

      onespell produces a subset of a panel data set in which all
      observations on varlist are non-missing and contiguous in the
      time dimension. If a panel unit  contains more than one such
      subset, the longest "spell" is retained.  Although performing
      this operation for a single variable of interest is fairly
      straightforward,  this routine deals with a more challenging
      task: generating the single longest spell in a listwise  fashion,
      across a set of variables. This applies the same logic as does,
      e.g., regress: an  observation with a missing value in any
      variable will be deleted from the regression sample. Some matrix
      software (e.g., DPD for Ox) requires that panel data be organized
      in this fashion,  with each unit appearing as a single contiguous
      block of non-missing observations. onespell  will produce such a
      dataset, which after conversion to Stata version 6 format  (by,
      e.g., Stat/Transfer) may be read directly by Ox. The routine has
      been tested with the latest  version of Ox (3.40) and the DPD
      package (1.21). The routine makes use of N.J. Cox's -tsspell-.

Available from SSC.

Kit Baum, Boston College Economics
http://ideas.repec.org/e/pba1.html

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