Year	Percent
1948	3.1
1949	4.4
1950	4.5
1951	4
1952	2.5
1953	2.5
1954	4.6
1955	3.8
1956	3.6
1957	3
1958	4.5
1959	4.1
1960	3.4
1961	4.5
1962	3.5
1963	3.6
1964	3.3
1965	2.8
1966	2.3
1967	2.4
1968	2.2
1969	2.2
1970	2.7
1971	3.3
1972	3.3
1973	2.8
1974	3.2
1975	5.1
1976	4.9
1977	4.4
1978	3.2
1979	3.2
1980	3.3
1981	3.8
1982	5.2
1983	5
1984	4.3
1985	4.3
1986	3.8
1987	3.1
1988	2.7
1989	2.8
1990	2.8
1991	3.4
1992	4.2
1993	4
1994	3.8014
1995	3.5908
1996	3.4019
1997	2.6429
1998	2.3712
1999	2.6313
2000	2.5218
2001	2.6927
2002	3.4759
2003	3.6958
2004	3.6462
2005	3.3456
2006	2.9277
2007	2.9785
2008	3.6746
2009	6.0065
2010	6.2365
2011	6.0946
2012	5.5696
2013	4.9918
2014	4.1843
2015	3.5983
2016	3.3005
2017	3.0564