Year	Percent
1960	11.98353
1961	13.02321
1962	14.29291
1963	14.10142
1964	14.87625
1965	16.0581
1966	16.86682
1967	15.17734
1968	16.1858
1969	17.0182
1970	17.45421
1971	17.15074
1972	18.05264
1973	18.9537
1974	23.21269
1975	20.92782
1976	22.17254
1977	21.24256
1978	19.8707
1979	20.3937
1980	23.60613
1981	25.94916
1982	26.58438
1983	28.6984
1984	30.49428
1985	30.06615
1986	24.84176
1987	26.20625
1988	26.65254
1989	28.03492
1990	26.79063
1991	26.66494
1992	26.07937
1993	27.14182
1994	31.28941
1995	34.48724
1996	35.6419
1997	36.76387
1998	40.29478
1999	37.86812
2000	45.5815
2001	43.34178
2002	41.23858
2003	40.22139
2004	41.22776
2005	41.60028
2006	42.89372
2007	43.43815
2008	42.9535
2009	34.72458
2010	40.61374
2011	45.909
2012	47.34878
2013	48.34814
2014	49.6372
2015	49.63256
2016	48.58783
2017	51.18131