Year	Percent
1967	18.11189
1968	14.77085
1969	13.86523
1970	14.66995
1971	12.78996
1972	16.98249
1973	16.30363
1974	20.77731
1975	22.39242
1976	19.37401
1977	19.02082
1978	18.47913
1979	22.75728
1980	24.09992
1981	23.01232
1982	21.7645
1983	22.97757
1984	22.62614
1985	22.81418
1986	22.6666
1987	21.00363
1988	21.67019
1989	21.74696
1990	23.37119
1991	18.55774
1992	20.52856
1993	22.44087
1994	19.04454
1995	19.42278
1996	21.42703
1997	20.77031
1998	17.52693
1999	16.96646
2000	14.68828
2001	15.71199
2002	15.31401
2003	16.12553
2004	14.63323
2005	19.56379
2006	21.54777
2007	19.77582
2008	23.21189
2009	19.6761
2010	19.35266
2011	18.97324
2012	20.40884
2013	20.05645
2014	18.65866
2015	17.05026
2016	16.1605
2017	17.55269