Year	Percent
1980	34.54756
1981	35.12101
1982	37.91707
1983	36.07391
1984	31.78074
1985	32.75218
1986	30.90857
1987	28.41825
1988	28.90404
1989	31.72207
1990	29.30533
1991	7.33876
1992	5.19999
1993	13.2
1994	17.9
1995	21
1996	21.15433
1997	20.491
1998	21.02356
1999	22.98639
2000	31.73425
2001	38.35997
2002	37.90222
2003	40.47286
2004	37.1998
2005	36.98518
2006	38.97967
2007	38.65553
2008	35.77843
2009	34.55779
2010	30.30868
2011	31.41358
2012	28.32855
2013	28.36917
2014	24.57535
2015	24.41346
2016	24.7787
2017	25.22404