Year	% of total
1989	100
1990	100
1991	100
1992	100
1993	100
1994	100
1995	100
1996	100
1997	100
1998	99.9
1999	99.9
2000	99.8
2001	99.8
2002	99.8
2003	99.8
2004	99.8
2005	99.8
2006	99.7
2007	99.7
2008	99.6
2009	99.6
2010	99.7
2011	99.9
2012	99.9
2013	99.8
2014	99.8
2017	99.8