Year	Percent
1960	7.82726
1961	7.72297
1962	7.67066
1963	7.64844
1964	7.6614
1965	7.69122
1966	7.7821
1967	3.94066
1968	4.00499
1969	3.9884
1970	3.92288
1971	3.81579
1972	3.76908
1973	3.87634
1974	4.19856
1975	4.63876
1976	5.11176
1977	5.45594
1978	5.59952
1979	5.47217
1980	5.19099
1981	4.97872
1982	4.76668
1983	4.62251
1984	4.59783
1985	4.65237
1986	4.71572
1987	4.74989
1988	4.75899
1989	4.75046
1990	4.72696
1991	4.70754
1992	3.16634
1993	2.73807
1994	2.69791
1995	2.63893
1996	2.58991
1997	2.53511
1998	2.48139
1999	2.42197
2000	2.36601
2001	2.30747
2002	2.25856
2003	2.22156
2004	2.2177
2005	2.28167
2006	2.34772
2007	2.41082
2008	2.47199
2009	2.53425
2010	2.59868
2011	2.65659
2012	2.71417
2013	2.76197
2014	2.79002
2015	2.81238
2016	2.83299
2017	2.85017