Year	Percent
1948	2.6
1949	4.6
1950	4
1951	2.2
1952	2.1
1953	2.2
1954	4.4
1955	3.2
1956	3
1957	3.1
1958	5.6
1959	4.2
1960	4.2
1961	5.1
1962	4
1963	3.8
1964	3.2
1965	2.7
1966	2.1
1967	1.9
1968	1.7
1969	1.6
1970	2.8
1971	3.5
1972	3.1
1973	2.5
1974	3.1
1975	5.7
1976	4.9
1977	4.3
1978	3.5
1979	3.4
1980	5.1
1981	5.5
1982	8
1983	8.2
1984	5.9
1985	5.6
1986	5.6
1987	5
1988	4.4
1989	4.1
1990	4.6
1991	5.9
1992	6.7
1993	6
1994	4.9143
1995	4.4142
1996	4.2159
1997	3.7636
1998	3.2599
1999	3.0087
2000	2.8727
2001	3.6801
2002	4.8463
2003	5.1907
2004	4.5543
2005	3.9431
2006	3.6198
2007	3.6885
2008	4.9782
2009	9.2338
2010	9.2914
2011	8.1973
2012	6.9255
2013	6.3611
2014	5.1513
2015	4.376
2016	4.0427
2017	3.6395