In what month and year did you start using [CURRENT METHOD] continuously?
Categories
Value
Category
1984
1986
1987
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
8888
D/K
9999
N/A
Sysmiss
Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.