Year	Percent
1976	34.09131
1977	40.25203
1978	33.0777
1979	31.54198
1980	37.17376
1981	46.02747
1982	39.44481
1983	33.01243
1984	29.91046
1985	21.0531
1986	19.83425
1987	22.55016
1988	22.66195
1989	23.23598
1990	30.79668
1991	24.96619
1992	33.47605
1993	36.62705
1994	33.29273
1995	32.9636
1996	30.52396
1997	25.72628
1998	21.8188
1999	21.57049
2000	22.36206
2001	21.05663
2002	20.0964
2003	20.84064
2004	27.38472
2005	34.14914
2006	28.34002
2007	30.26772
2008	29.89445
2009	26.2997
2010	24.02105
2011	25.45404
2012	26.89722
2013	28.05617
2014	27.97031
2015	24.10149
2016	22.184
2017	20.63605