Year	Percent
1980	37.16814
1981	36.58537
1982	36.15385
1983	37.12121
1984	35.46099
1985	31.91489
1986	34.30657
1987	35.21127
1988	35.37415
1989	34.72222
1990	33.33333
1991	31.77083
1992	22.92225
1993	19.24998
1994	23.3426
1995	31.67735
1996	40.92003
1997	44.35432
1998	47.17105
1999	48.27905
2000	52.32969
2001	51.96952
2002	51.37816
2003	50.51637
2004	50.93212
2005	49.97119
2006	54.44666
2007	55.88273
2008	59.54036
2009	59.408
2010	60.24895
2011	58.03287
2012	57.54444
2013	57.86319
2014	57.46509
2015	57.27377
2016	56.99691
2017	56.57581