Year	Percent
1960	17.02786
1961	18.01075
1962	17.89215
1963	17.77251
1964	17.8022
1965	18.93004
1966	19.7417
1967	19.86302
1968	19.2926
1969	19.44849
1970	23.94737
1971	21.87147
1972	21.25604
1973	22.10265
1974	25.40809
1975	32.42092
1976	37.60399
1977	31.64894
1978	29.50076
1979	36.39216
1980	46.61487
1981	50.89533
1982	52.56338
1983	54.32933
1984	56.58842
1985	53.9143
1986	32.64599
1987	35.78825
1988	29.91609
1989	37.97901
1990	40.64304
1991	36.03486
1992	35.51005
1993	35.29799
1994	45.48434
1995	44.8684
1996	51.84273
1997	56.86361
1998	46.05686
1999	61.27096
2000	72.15267
2001	65.48845
2002	63.31892
2003	61.17236
2004	65.86448
2005	71.88152
2006	75.50092
2007	73.24084
2008	77.41366
2009	71.11695
2010	75.3772
2011	76.62564
2012	74.76768
2013	72.0159
2014	69.41703
2015	54.67438
2016	50.20512
2017	54.26469