Year	Percent
1948	4.1
1949	6
1950	5.7
1951	4.4
1952	3.6
1953	3.3
1954	6
1955	4.9
1956	4.8
1957	4.7
1958	6.8
1959	5.9
1960	5.9
1961	7.2
1962	6.2
1963	6.5
1964	6.2
1965	5.5
1966	4.8
1967	5.2
1968	4.8
1969	4.7
1970	5.9
1971	6.9
1972	6.6
1973	6
1974	6.7
1975	9.3
1976	8.6
1977	8.2
1978	7.2
1979	6.8
1980	7.4
1981	7.9
1982	9.4
1983	9.2
1984	7.6
1985	7.4
1986	7.1
1987	6.2
1988	5.6
1989	5.4
1990	5.5
1991	6.4
1992	7
1993	6.6
1994	6.0528
1995	5.6713
1996	5.4696
1997	5.0736
1998	4.6201
1999	4.3383
2000	4.0984
2001	4.6538
2002	5.6129
2003	5.6653
2004	5.3982
2005	5.0965
2006	4.6274
2007	4.5017
2008	5.4216
2009	8.069
2010	8.6213
2011	8.4631
2012	7.893
2013	7.0757
2014	6.0603
2015	5.1785
2016	4.7888
2017	4.3086