http://www.icpsr.umich.edu/icpsrweb/ICPSR/studies/2756
data 11/19/1999
http://www.icpsr.umich.edu/icpsrweb/ICPSR/studies/2038
data 09/11/1998
http://www.icpsr.umich.edu/icpsrweb/ICPSR/studies/9028
data 02/13/1997
http://www.icpsr.umich.edu/icpsrweb/ICPSR/studies/6128
data 10/11/1993
http://www.icpsr.umich.edu/icpsrweb/ICPSR/studies/9508
data 05/03/1991
http://www.icpsr.umich.edu/icpsrweb/ICPSR/studies/9317
data 05/01/1990
http://www.icpsr.umich.edu/icpsrweb/ICPSR/studies/8451
data 01/06/1988