Year	Percent
1960	21.39133
1961	22.31892
1962	22.48872
1963	22.08679
1964	22.47265
1965	27.26826
1966	28.62078
1967	28.52366
1968	30.41126
1969	27.97904
1970	27.91148
1971	29.68536
1972	29.26526
1973	32.21918
1974	32.14113
1975	30.69395
1976	33.71662
1977	34.83079
1978	36.17518
1979	37.68599
1980	37.23694
1981	31.63682
1982	26.6747
1983	26.16185
1984	25.70051
1985	25.0996
1986	26.58527
1987	22.96207
1988	26.28905
1989	31.00445
1990	37.20188
1991	34.5225
1992	32.17021
1993	34.682
1994	39.83785
1995	43.69851
1996	46.85217
1997	46.18646
1998	46.42239
1999	41.02288
2000	53.97218
2001	51.3817
2002	52.73058
2003	54.09403
2004	58.42298
2005	59.00584
2006	56.05464
2007	53.50901
2008	51.32528
2009	39.53025
2010	45.75891
2011	51.25769
2012	50.9028
2013	47.94149
2014	47.56265
2015	45.16676
2016	42.61094
2017	43.56038