Year	Percent
1960	48.96969
1961	52.08184
1962	53.0944
1963	44.13914
1964	42.49423
1965	40.56105
1966	39.21009
1967	38.6415
1968	39.85635
1969	37.17942
1970	41.29394
1971	39.16187
1972	37.48562
1973	35.97238
1974	48.23861
1975	45.2475
1976	41.513
1977	42.77886
1978	43.66676
1979	47.32991
1980	55.26484
1981	58.75976
1982	59.82641
1983	56.71713
1984	52.57238
1985	49.97655
1986	50.40401
1987	49.0251
1988	56.20872
1989	65.31222
1990	72.42213
1991	81.4865
1992	74.62786
1993	79.02063
1994	90.75463
1995	98.02447
1996	90.19079
1997	92.37531
1998	93.74815
1999	96.25889
2000	100.59736
2001	92.96214
2002	91.05091
2003	87.25168
2004	95.00073
2005	90.95548
2006	90.39199
2007	86.29753
2008	77.16883
2009	71.14225
2010	71.01447
2011	69.68224
2012	68.54184
2013	67.09195
2014	64.51873
2015	62.94925
2016	60.97747
2017	64.44642