Year	Percent
1960	19.73094
1961	19.6986
1962	15.67623
1963	17.12062
1964	19.8741
1965	19.7774
1966	20.55138
1967	19.95413
1968	25.92593
1969	24.92153
1970	22.1585
1971	24.82303
1972	23.95714
1973	22.22878
1974	18.91111
1975	20.62589
1976	21.49159
1977	23.17832
1978	22.75705
1979	31.04905
1980	31.83897
1981	34.28328
1982	25.56364
1983	21.14341
1984	18.92104
1985	19.0657
1986	18.21851
1987	16.03194
1988	12.88108
1989	13.43002
1990	14.28283
1991	15.71499
1992	12.7655
1993	15.97858
1994	13.48975
1995	22.6569
1996	16.70013
1997	18.31233
1998	28.17997
1999	22.78514
2000	17.26179
2001	16.12959
2002	19.74052
2003	21.99496
2004	19.13146
2005	22.97821
2006	22.47665
2007	21.1464
2008	24.88393
2011	20.9973
2012	17.27265
2013	27.63316
2014	18.97896
2015	17.89235
2016	20