Year	Percent
1991	92.12598
1992	92.13069
1993	92.18417
1994	92.21676
1995	92.29514
1996	92.37017
1997	92.34791
1998	92.20783
1999	91.98392
2000	91.75291
2001	91.47986
2002	91.16612
2003	90.93239
2004	90.61616
2005	90.29923
2006	89.9171
2007	89.53176
2008	89.11331
2009	88.68239
2010	88.21653
2011	87.74586
2012	87.2409
2013	86.70726
2014	86.1851
2015	86.2868
2016	86.28199
2017	86.30679
2018	86.25312
2019	86.20693