Year	Percent
1976	33.9986
1977	33.60221
1978	33.84238
1979	32.91804
1980	32.93731
1981	32.54626
1982	31.76613
1983	31.29685
1984	30.11462
1985	30.44744
1986	30.25928
1987	29.75262
1988	29.51826
1989	29.28322
1990	29.56086
1991	29.50526
1992	29.0159
1993	28.30377
1994	28.4134
1995	28.85153
1996	28.75201
1997	28.67638
1998	28.51066
1999	28.42859
2000	28.2848
2001	28.20875
2002	27.38808
2003	27.49838
2004	27.37377
2005	27.07424
2006	27.25937
2007	27.57264
2008	26.96021
2009	25.79285
2010	25.53499
2011	25.44743
2012	25.63397
2013	25.52494
2014	25.36242
2015	25.02729
2016	24.71099
2017	25.26632