Year	Percent
1960	21.31398
1961	24.91922
1962	25.60921
1963	25.65202
1964	22.23516
1965	22.93769
1966	28.57873
1967	27.49107
1968	29.11987
1969	30.7357
1970	34.43437
1971	37.57122
1972	39.35826
1973	41.52846
1974	41.58314
1975	38.12492
1976	39.1238
1977	29.33532
1978	32.86736
1979	34.70514
1980	35.31145
1981	35.62885
1982	33.81248
1983	22.47102
1984	18.62682
1985	19.12101
1986	21.65171
1987	23.09452
1988	9.44043
1989	7.73179
1990	21.14069
1991	24.10736
1992	29.75866
1993	31.0612
1994	33.68337
1995	38.0441
1996	40.41417
1997	38.81298
1998	41.13719
1999	38.99192
2000	36.4897
2001	26.66105
2002	23.8083
2003	28.71406
2004	28.27163
2005	27.7506
2006	29.42239
2007	36.04422
2008	42.32787
2009	31.43168
2010	38.21286
2011	38.63746
2012	43.68882
2013	44.00799
2014	44.30866
2015	42.60027
2016	43.76244