Year	Percent
1960	2.62168
1961	4.04111
1962	3.8736
1963	3.94623
1964	4.96356
1965	7.13023
1966	8.44381
1967	9.11548
1968	10.14572
1969	10.61414
1970	11.44626
1971	12.68459
1972	16.61346
1973	23.94305
1974	22.25917
1975	22.68993
1976	25.55713
1977	26.02604
1978	24.91338
1979	23.46914
1980	28.45587
1981	29.95601
1982	27.36701
1983	27.98907
1984	29.42178
1985	27.33071
1986	32.47529
1987	34.88186
1988	33.0283
1989	27.85712
1990	25.3399
1991	24.1527
1992	24.62672
1993	24.13323
1994	24.24969
1995	25.93352
1996	25.28474
1997	28.97702
1998	40.3893
1999	33.56407
2000	35.00888
2001	32.73245
2002	30.82686
2003	32.70217
2004	38.295
2005	36.80966
2006	37.16626
2007	39.18468
2008	49.96141
2009	47.54976
2010	49.41949
2011	55.74747
2012	56.34024
2013	53.87508
2014	50.27553
2015	45.33669
2016	42.2842
2017	43.09098