Year	% of total
1991	97.8
1992	98
1993	97.8
1994	98.2
1995	96.2
1996	98.9
1997	99.6
1998	99.3
1999	99.4
2000	99.2
2001	99.7
2002	99.6
2003	99.6
2004	99.6
2005	99.7
2006	99.7
2007	99.9
2008	99.7
2009	99.9
2010	99.8
2011	99.7
2012	99.8
2013	99.7
2014	99.9
2015	100
2016	100
2017	99.8
2018	99.8
2019	99.6
2020	99.7
2021	99.6