Year	Percent
1980	35.70781
1981	35.63844
1982	34.28291
1983	37.14824
1984	40.13116
1985	42.79513
1986	40.03364
1987	40.7853
1988	45.56567
1989	46.42059
1990	33.11919
1991	43.47826
1992	47.11155
1993	38.20676
1994	45.04756
1995	51.92103
1996	58.97681
1997	50.10923
1998	43.08714
1999	43.16873
2000	36.47444
2001	35.14866
2002	33.90858
2003	34.68315
2004	41.27208
2005	42.86345
2006	47.32156
2007	52.38019
2008	52.54337
2009	42.33201
2010	50.17892
2011	59.06904
2012	60.80182
2013	64.65252
2014	65.01243
2015	64.1072
2016	63.97871
2017	66.32604