Year	Percent
1980	37.70276
1981	48.03859
1982	47.69615
1983	45.77205
1984	45.1304
1985	51.13761
1986	52.42133
1987	38.09134
1988	49.11632
1989	37.96755
1990	30.65261
1991	40.12281
1992	55.90385
1993	44.09362
1994	39.42604
1995	42.62953
1996	45.66832
1997	46.11598
1998	49.41759
1999	50.70118
2000	48.28762
2001	47.74815
2002	49.32872
2003	50.82834
2004	62.16442
2005	64.44833
2006	59.17786
2007	57.29552
2008	57.95919
2009	62.20415
2010	70.7312
2011	70.48617
2012	63.03859
2013	62.27557
2014	57.33798
2015	61.73077
2016	53.09316
2017	47.99129