Year	Percent
1960	32.31046
1961	29.99696
1962	28.61946
1963	30.40296
1964	29.85216
1965	29.29713
1966	28.55195
1967	27.33558
1968	27.66315
1969	27.55133
1970	27.15084
1971	26.82452
1972	26.40648
1973	27.97289
1974	30.65647
1975	29.37044
1976	28.23785
1977	28.35762
1978	27.41824
1979	29.23308
1980	32.50272
1981	36.07582
1982	35.87361
1983	35.92122
1984	36.29268
1985	36.43108
1986	32.29911
1987	31.70383
1988	33.61574
1989	35.41998
1990	36.42317
1991	37.68251
1992	36.95437
1993	36.56623
1994	36.85192
1995	36.61198
1996	37.06738
1997	37.76285
1998	37.18655
1999	39.34843
2000	44.84728
2001	45.55451
2002	45.70448
2003	43.83842
2004	43.92846
2005	47.45212
2006	50.73003
2007	51.48256
2008	54.17581
2009	47.12605
2010	50.52294
2011	53.82012
2012	54.6305
2013	54.82881
2014	54.61312
2015	55.67557
2016	53.58409
2017	55.2101