Year	Percent
1948	6.2
1949	9.4
1950	8.6
1951	6
1952	5.9
1953	5.5
1954	9
1955	7.8
1956	8.4
1957	8
1958	11.2
1959	10.4
1960	10.8
1961	12.7
1962	11.5
1963	12.4
1964	12
1965	10.9
1966	9.7
1967	9.7
1968	9.7
1969	9.1
1970	11
1971	12.6
1972	12.3
1973	11.2
1974	12.4
1975	15.5
1976	14.6
1977	14
1978	12.9
1979	12.2
1980	13
1981	14
1982	16.2
1983	15.8
1984	13.3
1985	13
1986	12.8
1987	11.7
1988	10.6
1989	10.4
1990	10.7
1991	12.5
1992	13.1
1993	12.3
1994	11.7985
1995	11.7706
1996	11.4278
1997	10.9292
1998	9.7574
1999	9.4617
2000	8.9223
2001	9.6119
2002	11.103
2003	11.4189
2004	10.9745
2005	10.1309
2006	9.6947
2007	9.4322
2008	11.1834
2009	14.886
2010	15.8355
2011	15.7302
2012	14.6614
2013	13.9252
2014	12.1731
2015	10.4017
2016	9.3404
2017	8.0882