Year	Percent
1948	3.4
1949	5.1
1950	4.8
1951	3.5
1952	3
1953	2.4
1954	4.4
1955	4
1956	3.5
1957	3.4
1958	5.2
1959	4.8
1960	4.2
1961	5.5
1962	4.6
1963	4.5
1964	4
1965	3.5
1966	3.1
1967	2.8
1968	2.8
1969	2.2
1970	3.3
1971	3.4
1972	3.6
1973	3
1974	3.3
1975	5.4
1976	5.1
1977	5.2
1978	4.2
1979	3.4
1980	3.1
1981	2.9
1982	3.7
1983	3.9
1984	3
1985	3.1
1986	3.2
1987	2.6
1988	2.5
1989	2.4
1990	3
1991	3.3
1992	3.3
1993	3.2
1994	3.999
1995	4.1778
1996	3.2732
1997	2.9761
1998	3.0648
1999	2.993
2000	3.3191
2001	2.957
2002	3.4412
2003	3.9922
2004	3.7172
2005	3.4498
2006	2.8281
2007	3.4002
2008	4.4634
2009	6.6892
2010	7.0782
2011	6.5386
2012	6.1507
2013	5.5268
2014	4.5593
2015	3.8123
2016	3.7566
2017	3.3829