Year	Percent
1960	2.00401
1961	2.07436
1962	2.7454
1963	4.02531
1964	3.81924
1965	3.87141
1966	3.57237
1967	3.22392
1968	3.24557
1969	3.14081
1970	3.18518
1971	3.65245
1972	3.71795
1973	3.15864
1974	3.20283
1975	3.5346
1976	3.47788
1977	3.16277
1978	3.12633
1979	3.26133
1980	3.13378
1981	3.18625
1982	3.34512
1983	3.32307
1984	3.41688
1985	3.56903
1986	4.10647
1987	4.23132
1988	3.72867
1989	3.53418
1990	3.24327
1991	3.00245
1992	2.79944
1993	2.92914
1994	2.75103
1995	2.65402
1996	2.54569
1997	2.72616
1998	2.80857
1999	3.06489
2000	3.05428
2001	2.93379
2002	2.8332
2003	2.68118
2004	2.82875
2005	2.75491
2006	2.52681
2007	2.34263
2008	2.55019
2009	2.8935
2010	2.70747
2011	2.65158
2012	2.53548
2013	2.46412
2014	2.48816
2015	2.40513
2016	2.50647
2017	2.49305