Year	Percent
1960	38.48526
1961	38.38669
1962	36.05625
1963	36.54165
1964	36.32824
1965	36.71724
1966	37.21708
1967	36.79755
1968	36.34385
1969	35.01805
1970	35.58626
1971	36.53608
1972	38.41148
1973	43.16067
1974	33.29842
1975	31.93263
1976	38.50013
1977	39.53054
1978	38.5028
1979	38.84322
1980	36.2069
1981	39.94991
1982	41.21715
1983	43.32425
1984	42.99459
1985	40.71795
1986	39.12442
1987	34.50359
1988	38.61769
1989	26.91191
1990	32.66518
1991	26.44777
1992	26.502
1993	24.17512
1994	22.24242
1995	21.87921
1996	22.67793
1997	25.92381
1998	28.98928
1999	30.07075
2000	33.15155
2001	35.08219
2002	34.70322
2003	35.4516
2004	34.94684
2005	37.92313
2006	44.0146
2007	42.26113
2008	41.26869
2009	42.33873
2010	43.13085
2011	42.76402
2012	42.42045
2013	43.19379
2014	44.55343
2015	43.76469
2016	41.11109
2017	41.83287