Year	Percent
1960	4.0489
1961	4.07379
1962	4.10881
1963	4.15778
1964	4.23308
1965	4.31081
1966	4.39864
1967	4.44541
1968	4.39086
1969	4.21521
1970	4.2263
1971	4.2578
1972	4.04277
1973	3.90439
1974	3.87645
1975	3.91427
1976	3.96701
1977	3.992
1978	3.9882
1979	3.38414
1980	2.6594
1981	2.59472
1982	2.54362
1983	2.50599
1984	2.48643
1985	2.4775
1986	2.46387
1987	2.4387
1988	2.41721
1989	2.94081
1990	3.76029
1991	3.26436
1992	3.46629
1993	3.38191
1994	3.06731
1995	2.90132
1996	2.99754
1997	2.95845
1998	2.67574
1999	2.13509
2000	2.43421
2001	2.30122
2002	2.25272
2003	2.18419
2004	2.16397
2005	2.16345
2006	2.21245
2007	2.40596
2008	2.57826
2009	2.64891
2010	3.77723
2011	3.06401
2012	1.2764
2013	1.36582
2014	1.49044
2015	1.54741
2016	1.54161
2017	1.48156