Year	Percent
1960	23.26193
1961	21.90191
1962	22.20172
1963	22.85788
1964	23.58618
1965	24.46902
1966	25.21686
1967	24.60429
1968	24.70471
1969	25.87726
1970	27.46863
1971	27.34512
1972	27.36535
1973	27.53745
1974	30.45336
1975	28.5045
1976	31.16376
1977	32.32364
1978	30.55289
1979	32.43644
1980	35.13193
1981	35.39589
1982	32.37562
1983	31.99399
1984	33.82399
1985	35.16184
1986	32.01688
1987	31.44752
1988	33.49162
1989	35.52316
1990	35.79095
1991	35.45792
1992	34.4749
1993	31.80115
1994	33.82856
1995	34.72346
1996	35.8344
1997	37.83961
1998	38.57613
1999	38.9031
2000	42.01422
2001	42.91911
2002	41.62878
2003	41.81697
2004	43.92513
2005	45.41405
2006	47.24664
2007	48.17238
2008	48.82482
2009	41.85481
2010	47.75764
2011	51.15412
2012	51.1785
2013	50.62512
2014	50.12953
2015	49.20452
2016	48.90518
2017	50.77139