Year	Percent
1960	14.30283
1961	13.47181
1962	15.2621
1963	15.93714
1964	21.39173
1965	22.43474
1966	22.68234
1967	22.79721
1968	20.9603
1969	20.45863
1970	19.10726
1971	19.64719
1972	21.33445
1973	20.93713
1974	21.04753
1975	15.98041
1976	13.65715
1977	14.43244
1978	15.75905
1979	21.19338
1980	21.45191
1981	20.32748
1982	20.68042
1983	24.54757
1984	29.175
1985	29.23775
1986	25.99083
1987	27.3343
1988	27.63236
1989	29.46059
1990	29.16463
1991	26.54342
1992	24.45485
1993	23.59646
1994	25.12964
1995	26.76555
1996	26.54681
1997	27.14542
1998	27.32184
1999	26.47187
2000	28.19086
2001	27.424
2002	26.94555
2003	26.75171
2004	27.25439
2005	26.73426
2006	29.91707
2007	31.00574
2008	31.12527
2009	27.08071
2010	29.87325
2011	34.29133
2012	37.71057
2013	39.51618
2014	40.07437
2015	40.40261
2016	40.12871
2017	43.11319