Year	Percent
1960	3.16122
1961	3.16995
1962	3.13852
1963	3.0299
1964	2.83289
1965	2.59161
1966	2.31325
1967	2.08745
1968	2.00979
1969	2.12215
1970	2.34955
1971	2.64348
1972	2.86215
1973	2.89206
1974	2.68202
1975	2.33736
1976	1.93475
1977	1.64665
1978	1.60251
1979	1.87784
1980	2.35344
1981	2.8796
1982	3.27824
1983	3.48164
1984	3.43774
1985	3.2373
1986	3.00611
1987	2.83713
1988	2.7278
1989	2.70352
1990	2.73307
1991	2.77257
1992	2.78243
1993	2.75894
1994	2.69199
1995	2.60084
1996	2.50493
1997	2.43272
1998	2.39977
1999	2.41627
2000	2.46509
2001	2.51754
2002	2.55651
2003	2.58743
2004	2.60556
2005	2.61238
2006	2.618
2007	2.61894
2008	2.60207
2009	2.56437
2010	2.51283
2011	2.45688
2012	2.40403
2013	2.35499
2014	2.31234
2015	2.27438
2016	2.23674
2017	2.19818