Year	Percent
1953	1.9
1954	2.4
1955	2.6
1956	2.3
1957	1.8
1958	2.2
1959	2.3
1960	1.6
1961	1.4
1962	1.2
1963	1.2
1964	1.1
1965	1.1
1966	1.3
1967	1.2
1968	1.2
1969	1.2
1970	1.2
1971	1.3
1972	1.5
1973	1.3
1974	1.4
1975	2
1976	2.2
1977	2.1
1978	2.4
1979	2.2
1980	2
1981	2.3
1982	2.4
1983	2.7
1984	2.7
1985	2.6
1986	2.7
1987	2.8
1988	2.5
1989	2.2
1990	2
1991	2
1992	2.1
1993	2.4
1994	2.8
1995	3.1
1996	3.4
1997	3.4
1998	4.2
1999	4.8
2000	4.9
2001	5.2
2002	5.5
2003	5.5
2004	4.9
2005	4.6
2006	4.3
2007	3.9
2008	4.1
2009	5.3
2010	5.4
2011	4.797
2012	4.6
2013	4.3
2014	3.7
2015	3.6
2016	3.3
2017	3