Year	Percent
1960	4.31266
1961	4.09789
1962	3.65587
1963	3.64841
1964	3.86589
1965	5.90467
1966	6.73052
1967	5.4046
1968	5.10391
1969	5.51204
1970	6.15839
1971	6.73553
1972	6.86596
1973	6.21064
1974	6.091
1975	6.32152
1976	5.88947
1977	5.54741
1978	5.5033
1979	5.45327
1980	5.52324
1981	5.71087
1982	6.37572
1983	6.6438
1984	6.65949
1985	6.92213
1986	6.99166
1987	6.97188
1988	6.78581
1989	6.53273
1990	6.52232
1991	6.57095
1992	6.69819
1993	6.42731
1994	5.92355
1995	5.82023
1996	5.62823
1997	5.34665
1998	5.16373
1999	4.50882
2000	3.96964
2001	4.06348
2002	4.19155
2003	4.08892
2004	3.96199
2005	3.86604
2006	3.6757
2007	3.43099
2008	3.1396
2009	3.07125
2010	3.0715
2011	3.13389
2012	3.29231
2013	3.26783
2014	3.32314
2015	3.41423
2016	3.37147
2017	3.49548