Year	Percent
1960	5.8301
1961	5.84922
1962	5.87084
1963	5.87878
1964	6.50311
1965	8.42406
1966	8.34525
1967	8.27485
1968	8.26065
1969	8.28076
1970	8.38204
1971	8.48147
1972	8.55627
1973	8.19448
1974	8.07678
1975	7.88407
1976	7.68586
1977	7.50832
1978	7.41474
1979	2.98122
1980	3.08809
1981	3.18408
1982	3.28517
1983	3.41391
1984	3.58648
1985	3.75894
1986	3.95766
1987	4.11577
1988	4.2272
1989	4.25217
1990	4.22967
1991	4.20576
1992	4.18794
1993	4.01224
1994	3.39898
1995	3.47354
1996	3.53
1997	3.57117
1998	3.64155
1999	3.73001
2000	3.82376
2001	3.92169
2002	3.98254
2003	3.98255
2004	3.89593
2005	3.7618
2006	3.61288
2007	3.49703
2008	3.42045
2009	3.41038
2010	3.51954
2011	3.63475
2012	3.73124
2013	3.79426
2014	3.82052
2015	3.82808
2016	3.83104
2017	3.84406