Year	Percent
1948	2.3
1949	3.8
1950	3.4
1951	2.9
1952	2.2
1953	1.4
1954	3
1955	2.3
1956	2.3
1957	3.4
1958	3.7
1959	2.8
1960	2.9
1961	4
1962	4.2
1963	3.2
1964	3.3
1965	2.9
1966	2.8
1967	2.7
1968	2.7
1969	2.3
1970	3.1
1971	3.6
1972	3.5
1973	2.9
1974	3.6
1975	5
1976	5
1977	4.7
1978	3.8
1979	3.3
1980	3.1
1981	3.6
1982	3.2
1983	3.4
1984	3.8
1985	3.3
1986	2.8
1987	2.4
1988	2.9
1989	2.9
1990	3.1
1991	3.3
1992	4.5
1993	3.1
1994	3.9253
1995	3.611
1996	3.8215
1997	3.5481
1998	3.3058
1999	3.2101
2000	2.7331
2001	2.9376
2002	3.9242
2003	3.6181
2004	3.4047
2005	3.5202
2006	2.9907
2007	3.1121
2008	3.9407
2009	6.1293
2010	6.212
2011	6.5348
2012	6.3101
2013	5.1217
2014	4.7
2015	3.8554
2016	3.9151
2017	3.8397