Year	Percent
1960	11.97967
1961	13.9632
1962	15.59826
1963	14.65659
1964	12.38118
1965	14.33263
1966	18.2208
1967	19.6846
1968	22.64261
1969	22.45847
1970	21.13568
1971	23.03615
1972	21.46345
1973	27.69021
1974	33.35195
1975	31.37619
1976	28.39064
1977	27.91369
1978	29.24977
1979	30.91757
1980	37.12723
1981	37.20542
1982	32.9025
1983	30.05605
1984	28.53231
1985	25.89065
1986	28.2634
1987	28.34568
1988	26.35802
1989	25.69411
1990	25.9211
1991	26.23658
1992	24.86184
1993	23.45417
1994	24.62581
1995	26.8516
1996	28.21964
1997	29.65596
1998	29.59847
1999	27.872
2000	32.93831
2001	31.17862
2002	29.32685
2003	30.69083
2004	34.46608
2005	34.37465
2006	36.38509
2007	38.05833
2008	49.97215
2009	42.86288
2010	46.23459
2011	54.25258
2012	53.54596
2013	48.89567
2014	45.02169
2015	38.37543
2016	35.42863
2017	37.68824