Year	% of total
1988	77.4
1996	87
2000	98.5
2001	92
2002	96.5
2003	96.1
2004	97.3
2005	94
2006	99.3
2007	94.6
2008	98.3
2009	99.5
2010	99.1
2011	99.8
2012	99.8
2013	99.9
2014	99.5
2015	99.7
2016	99.7
2017	99.8