6/12/2001 = Start date of this file by Jean Roth, jroth@nber.org 

2005-05-17 -- 2001 and 2002 data, docs & SAS programs added.  

2003-12-04 -- 2000 data & docs files.  Source http://www.nber.org/data/citenchs.html
              SAS programs added.

2002-09-23 -- Pkzipped documentation added.

5/29/2002 -- 1998 and 1999 Data files and SAS programs added.

9/10/2001 -- Value labels added to SAS file;
             Carriage Return & line feed characters added after each record.
             Revised SAS file incorporates this change.