Year	Percent
1960	20.02988
1961	23.10522
1962	26.54177
1963	27.4755
1964	29.11518
1965	27.51285
1966	28.0055
1967	29.37225
1968	28.29036
1969	25.20422
1970	34.05085
1971	32.71355
1972	31.41004
1973	36.54847
1974	44.96217
1975	40.62154
1976	37.99752
1977	37.64785
1978	37.63165
1979	40.65247
1980	43.25352
1981	39.65055
1982	35.6272
1983	38.74181
1984	37.27017
1985	32.75164
1986	34.03269
1987	38.53785
1988	41.58062
1989	44.45313
1990	47.75048
1991	47.6886
1992	47.5986
1993	54.99734
1994	56.09004
1995	61.84971
1996	65.82405
1997	77.12013
1998	84.35467
1999	83.3109
2000	94.79638
2001	88.62203
2002	93.78344
2003	93.92019
2004	93.88365
2005	88.03795
2006	83.04354
2007	72.61746
2008	62.85893
2009	50.08687
2010	55.09463
2011	49.96705
2012	46.96221
2013	45.02839
2014	45.9636
2015	45.625
2016	48.16215
2017	51.57272