Year	Percent
1960	19.85998
1961	20.64785
1962	20.46566
1963	20.81142
1964	22.03316
1965	14.94431
1966	15.98722
1967	15.36046
1968	16.75302
1969	17.50102
1970	20.43338
1971	21.90704
1972	21.55288
1973	21.19055
1974	23.94439
1975	23.14525
1976	25.4814
1977	25.88181
1978	25.50647
1979	26.88255
1980	25.32901
1981	25.81544
1982	26.718
1983	26.14627
1984	28.04332
1985	27.66264
1986	25.893
1987	25.77237
1988	28.30348
1989	27.71474
1990	28.60788
1991	28.97355
1992	30.13092
1993	26.36306
1994	25.47539
1995	24.65339
1996	24.44092
1997	23.45349
1998	23.24819
1999	25.90863
2000	33.61759
2001	29.0496
2002	28.80796
2003	27.9993
2004	29.7117
2005	31.54458
2006	33.88671
2007	34.45813
2008	37.91931
2009	32.41761
2010	34.72419
2011	37.63464
2012	37.75527
2013	37.14613
2014	36.77882
2015	31.87213
2016	32.32037
2017	31.4252