Year	Percent
1948	3.1
1949	5.4
1950	4.9
1951	2.8
1952	2.4
1953	2.8
1954	4.5
1955	4.3
1956	3.5
1957	3.5
1958	5.5
1959	4.5
1960	4.6
1961	5.7
1962	4.6
1963	4.3
1964	3.9
1965	3.3
1966	2.6
1967	2.3
1968	1.9
1969	1.8
1970	2.8
1971	3.3
1972	3.2
1973	2.4
1974	2.6
1975	4.3
1976	4.2
1977	3.6
1978	2.8
1979	2.7
1980	3.4
1981	3.6
1982	5.5
1983	6.1
1984	5
1985	4.3
1986	4.3
1987	3.7
1988	3.5
1989	3.5
1990	3.8
1991	4.6
1992	5.8
1993	5.2
1994	4.3669
1995	3.5919
1996	3.4652
1997	3.1536
1998	2.7741
1999	2.7183
2000	2.4276
2001	3.3257
2002	4.2576
2003	4.5003
2004	3.9074
2005	3.2986
2006	3.0223
2007	3.197
2008	3.7504
2009	7.1572
2010	7.9518
2011	7.1531
2012	6.2957
2013	5.6653
2014	4.5084
2015	3.9384
2016	3.7878
2017	3.1488