Year	Percent
1980	13.64521
1981	15.43993
1982	13.69774
1983	12.05919
1984	12.9308
1985	14.99298
1986	17.6309
1987	23.54716
1988	28.07272
1989	28.04786
1990	26.83037
1991	32.15822
1992	31.98648
1993	31.56841
1994	29.52874
1995	37.76894
1996	35.48813
1997	35.90472
1998	33.10001
1999	31.11449
2000	29.37723
2001	26.28617
2002	23.87155
2003	25.52907
2004	31.02749
2005	38.24974
2006	54.41944
2007	54.96856
2008	48.79026
2009	44.70198
2010	42.45279
2011	41.20541
2012	38.72533
2013	40.4599
2014	36.28464
2015	33.22427
2016	29.718
2017	26.04065