Year	Percent
1960	2.14678
1961	2.13048
1962	2.123
1963	2.14096
1964	2.19214
1965	2.26303
1966	2.33677
1967	2.39494
1968	2.43128
1969	2.43945
1970	2.42785
1971	2.41014
1972	2.39535
1973	2.38179
1974	2.37185
1975	2.36347
1976	2.3478
1977	2.32677
1978	2.31031
1979	2.30031
1980	2.29105
1981	2.27956
1982	2.25552
1983	2.20936
1984	2.13664
1985	2.04484
1986	1.95548
1987	1.86852
1988	1.76566
1989	1.64464
1990	1.51635
1991	1.37849
1992	1.25767
1993	1.18759
1994	1.18332
1995	1.22298
1996	1.27661
1997	1.31169
1998	1.31738
1999	1.28069
2000	1.21359
2001	1.14866
2002	1.09255
2003	1.0229
2004	0.93798
2005	0.84699
2006	0.74769
2007	0.66337
2008	0.62476
2009	0.64653
2010	0.71072
2011	0.78868
2012	0.85383
2013	0.90142
2014	0.92092
2015	0.9192
2016	0.91474
2017	0.91362