Year	Percent
1960	28.93741
1961	29.79655
1962	29.61694
1963	29.60707
1964	31.58403
1965	31.71021
1966	33.24545
1967	33.6875
1968	35.96926
1969	36.42291
1970	35.3514
1971	35.10115
1972	36.45372
1973	38.95026
1974	42.86301
1975	40.37224
1976	39.13401
1977	40.46445
1978	43.31878
1979	47.28465
1980	47.57209
1981	46.61302
1982	41.26294
1983	41.56187
1984	47.2915
1985	47.04234
1986	46.58329
1987	44.22759
1988	45.29694
1989	42.76109
1990	42.23952
1991	41.28025
1992	44.51426
1993	49.24245
1994	55.42747
1995	59.70267
1996	59.94641
1997	63.61502
1998	66.53754
1999	67.83623
2000	70.24459
2001	66.15459
2002	63.31454
2003	58.02006
2004	58.31659
2005	58.39839
2006	56.80164
2007	55.35114
2008	56.51436
2009	47.11368
2010	48.97358
2011	51.15454
2012	51.08225
2013	50.69362
2014	52.83435
2015	53.79149
2016	52.30412
2017	52.18193