Year	Percent
1960	18.36883
1961	17.56373
1962	16.45495
1963	18.3734
1964	18.86466
1965	20.26084
1966	19.45645
1967	20.15648
1968	19.38932
1969	19.6648
1970	22.73919
1971	20.24176
1972	20.31324
1973	21.3821
1974	23.17229
1975	23.69229
1976	22.28856
1977	22.84571
1978	23.60549
1979	25.94665
1980	27.15848
1981	27.38402
1982	22.91086
1983	20.75042
1984	19.86092
1985	21.17553
1986	18.53812
1987	19.2606
1988	22.56088
1989	22.94289
1990	23.1416
1991	23.32859
1992	23.29164
1993	23.02058
1994	24.92335
1995	20.96587
1996	21.57212
1997	22.59693
1998	23.69316
1999	22.57877
2000	22.95818
2001	20.83501
2002	20.70578
2003	21.09587
2004	21.49499
2005	22.12623
2006	22.82292
2007	23.11881
2008	24.10684
2009	22.88892
2010	22.7931
2011	23.28121
2012	23.88655
2013	22.49338
2014	21.90538
2015	23.27184
2016	23.74463
2017	23.1474