Year	Percent
1960	14.7397
1961	15.79656
1962	16.85682
1963	18.46267
1964	19.03319
1965	18.56332
1966	19.08813
1967	17.97941
1968	17.95457
1969	19.97567
1970	20.26221
1971	20.94401
1972	19.65852
1973	19.93929
1974	20.31248
1975	21.85167
1976	22.32016
1977	20.76756
1978	20.66784
1979	21.53258
1980	22.37984
1981	20.13437
1982	20.05806
1983	19.89423
1984	20.24764
1985	20.22632
1986	21.16486
1987	21.62525
1988	21.69121
1989	21.20182
1990	22.3613
1991	22.63712
1992	22.24827
1993	22.09399
1994	21.77408
1995	21.32329
1996	21.99438
1997	21.55728
1998	22.05302
1999	22.10317
2000	21.71565
2001	22.38222
2002	22.21931
2003	22.23118
2004	25.12128
2005	25.52832
2006	19.67047
2007	19.98117
2008	21.7374
2009	19.19149
2010	19.71948
2011	20.50179
2012	21.29881
2013	20.21694
2014	20.02516
2015	19.091
2016	18.2571
2017	17.94227