Year	Percent
1960	11.91072
1961	11.53417
1962	17.79548
1963	18.64766
1964	17.72709
1965	18.8535
1966	19.94137
1967	23.689
1968	29.80443
1969	29.15937
1970	21.74386
1971	23.80385
1972	24.4143
1973	23.61826
1974	22.84311
1975	24.05588
1976	27.67862
1977	32.10697
1978	38.35111
1979	35.39907
1980	37.15061
1981	35.97641
1982	31.0225
1983	28.48216
1984	33.0366
1985	37.09608
1986	32.79708
1987	32.37437
1988	29.19779
1989	31.39394
1990	29.70802
1991	25.49078
1992	26.02636
1993	27.74992
1994	27.7556
1995	27.4775
1996	27.06077
1997	27.88529
1998	28.57446
1999	32.62046
2000	35.56961
2001	31.31301
2002	32.89979
2003	34.65876
2004	39.12796
2005	40.79187
2006	40.80078
2007	40.51978
2008	38.51362
2009	33.33218
2010	34.99117
2011	35.99125
2012	36.05054
2013	33.26772
2014	32.21466
2015	31.27073
2016	30.26729