Year	Percent
1976	22.56665
1977	22.69975
1978	23.34265
1979	22.61779
1980	22.43058
1981	21.72711
1982	21.4753
1983	20.81556
1984	22.76556
1985	25.05275
1986	27.10384
1987	27.95581
1988	27.98164
1989	27.95539
1990	27.78398
1991	28.17259
1992	28.57236
1993	28.366
1994	28.14616
1995	28.39158
1996	28.33166
1997	27.22677
1998	27.10916
1999	27.14939
2000	27.08745
2001	27.73725
2002	26.94578
2003	26.45085
2004	25.29073
2005	24.13224
2006	22.33634
2007	22.54527
2008	23.33758
2009	23.34965
2010	22.47197
2011	21.59977
2012	20.93976
2013	20.6006
2014	19.83258
2015	19.24209
2016	18.57509
2017	18.17846