Year	Percent
1960	4.00495
1961	3.97313
1962	4.77634
1963	5.2048
1964	4.65771
1965	4.34619
1966	4.15308
1967	4.33196
1968	3.61881
1969	3.61056
1970	3.2005
1971	3.25105
1972	3.36503
1973	3.35665
1974	3.46451
1975	3.48796
1976	3.3311
1977	3.22776
1978	3.23961
1979	3.14903
1980	3.14602
1981	3.23157
1982	3.22352
1983	3.21574
1984	3.1087
1985	3.04619
1986	2.96433
1987	2.94518
1988	2.8056
1989	2.69035
1990	2.67548
1991	2.12242
1992	1.9765
1993	1.79915
1994	1.64695
1995	1.58825
1996	1.55727
1997	1.49719
1998	1.47763
1999	1.48207
2000	1.44362
2001	1.40597
2002	1.41077
2003	1.39905
2004	1.34809
2005	1.32994
2006	1.26878
2007	1.23705
2008	1.28132
2009	1.38891
2010	1.35365
2011	1.28111
2012	1.31126
2013	1.22399
2014	1.18497
2015	1.17947
2016	1.19585
2017	1.22014