Year	% of total
1991	99.6
1992	99.3
1993	99.3
1994	99.4
1995	99.3
1996	99.3
1997	99.3
1998	99.3
1999	99.3
2000	99.3
2001	99.3
2002	99.3
2003	99.3
2004	99.3
2005	99.4
2006	99.3
2007	99.2
2008	99.1
2009	99.1
2010	99.1
2011	99.1
2012	99.2
2013	99
2014	99.8
2015	98.8
2016	98.8
2017	99.4
2018	98.7
2019	98.8
2020	96