Year	Percent
1965	46.96742
1966	47.48923
1967	48.76249
1968	48.99615
1969	49.84272
1970	50
1971	49.76515
1972	49.17891
1973	50.5899
1974	52.59002
1975	52.6376
1976	53.4296
1977	47.96163
1978	52.6896
1979	48.53467
1980	39.55254
1981	37.65809
1982	36.97584
1983	39.08327
1984	35.82629
1985	40.54842
1986	42.60176
1987	43.61916
1988	44.81562
1989	43.21255
1990	44.88785
1991	44.69792
1992	45.77348
1993	50.54525
1994	47.14993
1995	48.31044
1996	47.56983
1997	46.70822
1998	47.02312
1999	46.33831
2000	45.46312
2001	48.11334
2002	48.60683
2003	49.21792
2004	50.44632
2005	50.65705
2006	49.46663
2007	49.66851
2008	50.75745
2009	52.57754
2010	52.12941
2011	53.06961
2012	51.95643
2013	52.46889
2014	51.83512
2015	52.07602
2016	52.18101
2017	52.67247