Year	Percent
1960	13.89841
1961	12.18417
1962	14.89362
1963	15.95563
1964	14.61707
1965	14.61712
1966	16.03782
1967	19.6539
1968	18.49876
1969	19.37126
1970	20.8852
1971	17.09986
1972	15.94023
1973	19.06849
1974	26.19623
1975	18.95018
1976	19.21365
1977	23.0608
1978	26.56129
1979	26.78215
1980	24.76617
1981	21.06757
1982	14.10367
1983	13.84465
1984	17.41488
1985	17.32381
1986	13.8506
1987	17.4112
1988	20.99233
1989	19.1407
1990	22.97998
1991	24.65367
1992	25.96277
1993	33.55811
1994	37.63079
1995	31.55678
1996	31.1287
1997	32.16843
1998	30.92649
1999	34.67365
2000	28.28843
2001	26.00094
2002	24.25844
2003	25.28088
2004	29.66556
2005	27.62298
2006	28.34193
2007	33.6653
2008	36.06597
2009	20.59944
2010	21.87984
2011	25.99999
2012	24.56421
2013	21.76035
2014	22.18383
2015	25.118
2016	23.31814
2017	23.77534