Year	Percent
1960	6.81535
1961	3.46551
1962	3.50495
1963	3.54425
1964	3.55524
1965	3.55742
1966	3.57323
1967	3.58534
1968	3.61101
1969	3.64068
1970	3.68552
1971	4.49745
1972	4.52756
1973	4.58746
1974	4.71264
1975	4.8499
1976	5.00735
1977	5.11538
1978	5.14463
1979	5.06738
1980	4.93631
1981	5.85593
1982	5.7206
1983	5.62126
1984	5.59113
1985	5.58432
1986	5.59676
1987	5.591
1988	5.56443
1989	5.5074
1990	5.44311
1991	4.20296
1992	4.16787
1993	4.13575
1994	4.11217
1995	4.09833
1996	4.09013
1997	4.07071
1998	4.06044
1999	4.05584
2000	4.05382
2001	4.86279
2002	4.84605
2003	4.83305
2004	4.82485
2005	4.81599
2006	4.81001
2007	4.80108
2008	4.78911
2009	4.76356
2010	4.7416
2011	4.69199
2012	4.64174
2013	4.58182
2014	4.51567
2015	4.44593
2016	4.36999
2017	4.30136