Year	Percent
1948	3.5
1949	5
1950	4.9
1951	4
1952	3.1
1953	2.8
1954	5.5
1955	4.3
1956	4.1
1957	4
1958	6.1
1959	5
1960	5
1961	6.2
1962	5.2
1963	5.3
1964	5
1965	4.3
1966	3.6
1967	4.1
1968	3.4
1969	3.5
1970	4.5
1971	5.3
1972	4.9
1973	4.4
1974	4.9
1975	7.5
1976	6.8
1977	6.4
1978	5.5
1979	5.2
1980	6
1981	6.3
1982	7.7
1983	7.7
1984	6.3
1985	6.2
1986	5.9
1987	5.1
1988	4.6
1989	4.4
1990	4.6
1991	5.4
1992	6
1993	5.7
1994	5.0513
1995	4.5998
1996	4.4424
1997	4.1177
1998	3.7876
1999	3.4289
2000	3.2733
2001	3.8823
2002	4.7755
2003	4.8119
2004	4.5533
2005	4.3726
2006	3.9229
2007	3.8022
2008	4.6256
2009	7.1888
2010	7.8076
2011	7.622
2012	7.1213
2013	6.2531
2014	5.3139
2015	4.5587
2016	4.2751
2017	3.873