Year	Percent
1960	11.55614
1961	16.86351
1962	18.18141
1963	20.88155
1964	20.51496
1965	21.46808
1966	15.9609
1967	16.70023
1968	18.01947
1969	14.7531
1970	15.793
1971	15.63175
1972	14.17552
1973	12.93048
1974	13.37202
1975	16.22753
1976	17.24334
1977	19.26971
1978	17.85805
1979	17.87514
1980	18.4818
1981	18.77417
1982	19.26123
1983	18.79979
1984	18.27052
1985	18.32018
1986	18.77434
1987	19.13433
1988	18.01421
1989	18.91146
1990	18.93537
1991	19.0264
1992	20.23674
1993	20.81826
1994	19.54642
1995	18.54552
1996	18.99666
1997	17.9192
1998	17.7112
1999	15.56494
2000	17.22663
2001	16.99636
2002	16.58276
2003	16.75802
2004	16.57801
2005	19.08126
2006	19.332
2007	18.78707
2008	19.20584
2009	17.54948
2010	15.80456
2011	14.12063
2012	15.07596
2013	14.95733
2014	14.63527
2015	15.70703
2016	15.68612
2017	16.09436