Year	Percent
1960	12.63894
1961	11.95319
1962	11.78734
1963	14.28571
1964	15.38758
1965	16.78684
1966	18.9401
1967	16.20915
1968	16.73393
1969	17.80343
1970	18.57143
1971	17.28638
1972	18.90734
1973	20.88199
1974	22.40709
1975	21.72303
1976	21.5724
1977	24.4558
1978	21.47564
1979	21.34848
1980	22.1864
1981	17.08975
1982	14.7872
1983	12.99447
1984	13.00211
1985	11.94823
1986	16.0519
1987	15.84891
1988	16.10368
1989	17.30745
1990	21.02752
1991	17.95261
1992	18.06599
1993	17.70303
1994	17.51994
1995	19.25904
1996	17.81012
1997	17.95611
1998	18.17161
1999	19.00492
2000	20.19503
2001	28.20745
2002	26.29895
2003	25.77367
2004	26.9755
2005	25.05468
2006	24.93173
2007	25.56526
2008	24.7182
2009	23.97537
2010	25.80563
2011	26.62528
2012	24.86858
2013	23.71986
2014	23.15842
2015	21.16045
2016	19.5421
2017	18.79601