Year	Percent
1991	68.81572
1992	69.49483
1993	68.11944
1994	70.89339
1995	74.9322
1996	74.37354
1997	75.07465
1998	75.58891
1999	75.92591
2000	76.46127
2001	76.18299
2002	78.05032
2003	78.49992
2004	78.85164
2005	79.29378
2006	80.14543
2008	80.7926
2009	80.15128
2010	80.7083
2011	81.32071
2012	81.29737
2013	80.8734
2014	80.46651
2017	78.50095