Year	Percent
1991	64.26087
1992	63.30268
1993	63.34998
1994	63.37958
1995	63.13507
1996	63.75186
1997	63.64428
1998	64.95412
1999	65.89209
2000	66.15586
2001	67.43669
2002	67.52175
2003	67.87311
2004	67.71395
2005	68.1403
2006	67.63687
2007	68.09687
2008	68.55006
2009	68.07256
2010	68.09341
2011	67.04208
2012	66.70286
2013	67.07687
2014	67.84427
2015	68.4823
2016	69.7185
2017	69.47884