Year	Percent
1960	23.65297
1961	23.4019
1962	26.43156
1963	28.82429
1964	28.87397
1965	29.30052
1966	27.11517
1967	26.46189
1968	26.68487
1969	24.38596
1970	26.7324
1971	26.29969
1972	35.28925
1973	28.21032
1974	29.07489
1975	28.04276
1976	32.99472
1977	32.09133
1978	34.4097
1979	42.02458
1980	24.2288
1981	22.34417
1982	15.97882
1983	19.40031
1984	16.44304
1985	14.7662
1986	12.77631
1987	11.77068
1988	17.98088
1989	32.53701
1990	24.94836
1991	21.82198
1992	17.25123
1993	20.42793
1994	13.13988
1995	16.09509
1996	16.84736
1997	19.41955
1998	19.33444
1999	18.53028
2000	20.10817
2001	19.04191
2002	18.84714
2003	20.705
2004	23.05986
2005	24.38213
2006	31.26663
2007	33.06357
2008	34.47046
2009	33.98149
2010	40.46712
2011	45.01698
2012	47.46918
2013	45.21427
2014	45.00807
2015	40.55086
2016	39.10199
2017	41.22685