Year	Percent
1960	4.45388
1961	4.45558
1962	4.48103
1963	4.53064
1964	4.56368
1965	4.60019
1966	4.63728
1967	6.96818
1968	7.27884
1969	7.32392
1970	7.36115
1971	7.38993
1972	7.44091
1973	7.47153
1974	7.52662
1975	7.56088
1976	7.64774
1977	7.73938
1978	5.97886
1979	5.3903
1980	5.24623
1981	4.96027
1982	4.77527
1983	5.0164
1984	5.77316
1985	6.77836
1986	7.89021
1987	8.57775
1988	8.88685
1989	7.951
1990	6.4813
1991	4.90703
1992	3.67775
1993	3.01309
1994	3.16177
1995	3.85864
1996	4.72737
1997	5.35563
1998	5.7543
1999	4.07808
2000	3.56433
2001	3.37193
2002	3.27825
2003	3.25302
2004	3.31012
2005	3.42825
2006	3.53972
2007	3.61883
2008	3.65679
2009	3.72927
2010	3.77137
2011	3.81124
2012	3.85058
2013	3.90653
2014	3.95729
2015	4.03013
2016	4.08095
2017	4.14256