Year	Percent
1960	4.7433
1961	4.81648
1962	4.85573
1963	4.82682
1964	4.754
1965	4.64521
1966	4.50715
1967	4.4106
1968	4.40122
1969	4.44472
1970	4.58867
1971	4.71418
1972	4.79611
1973	4.8568
1974	4.84374
1975	4.7845
1976	4.76576
1977	4.69864
1978	4.61769
1979	4.90344
1980	5.23314
1981	5.06213
1982	4.9138
1983	4.82034
1984	4.77728
1985	4.77582
1986	4.77756
1987	4.76892
1988	4.8151
1989	4.79532
1990	4.12502
1991	4.28678
1992	4.41831
1993	4.38809
1994	4.2036
1995	3.90144
1996	3.57305
1997	3.30953
1998	3.2115
1999	3.27417
2000	3.3825
2001	3.54171
2002	3.71082
2003	3.82829
2004	3.83972
2005	3.79081
2006	3.74401
2007	3.70105
2008	3.67076
2009	3.63359
2010	3.08149
2011	2.73719
2012	2.70031
2013	2.66441
2014	2.63411
2015	2.59982
2016	2.57084
2017	2.53949