Year	Percent
1960	4.79348
1961	4.60339
1962	4.47788
1963	4.43566
1964	4.46413
1965	4.57156
1966	4.66469
1967	4.71221
1968	4.73609
1969	4.72184
1970	4.68423
1971	4.63165
1972	4.57029
1973	4.46479
1974	4.31392
1975	4.14353
1976	3.9733
1977	3.81916
1978	3.64279
1979	3.46946
1980	3.29847
1981	3.1147
1982	2.97551
1983	2.87302
1984	2.83082
1985	2.83934
1986	2.83673
1987	2.83847
1988	2.83623
1989	2.84551
1990	2.84989
1991	2.85283
1992	2.84672
1993	2.80306
1994	2.72179
1995	2.61367
1996	2.4946
1997	2.38006
1998	2.27618
1999	2.18967
2000	2.10825
2001	2.04237
2002	1.96517
2003	1.8628
2004	1.72087
2005	1.5552
2006	1.38483
2007	1.23848
2008	1.16376
2009	1.18477
2010	1.26614
2011	1.36738
2012	1.44504
2013	1.48191
2014	1.46512
2015	1.40805
2016	1.34503
2017	1.29149