Year	Percent
1948	8
1949	11.7
1950	9.7
1951	5.5
1952	6.4
1953	6.3
1954	11.9
1955	9.3
1956	8.6
1957	9.6
1958	14.4
1959	11.3
1960	11.5
1961	13.3
1962	11.2
1963	12.1
1964	11.1
1965	9.5
1966	7.7
1967	7.9
1968	7.8
1969	7.8
1970	11.1
1971	12.8
1972	11.9
1973	9.9
1974	11.5
1975	16.6
1976	14.8
1977	13.3
1978	11.7
1979	11.4
1980	14.6
1981	15.7
1982	19.1
1983	18.4
1984	14.4
1985	14.1
1986	13.7
1987	12.6
1988	11.4
1989	11.4
1990	11.6
1991	14.3
1992	15.3
1993	14.3
1994	13.1992
1995	12.5576
1996	12.7221
1997	11.9053
1998	11.0633
1999	10.2976
2000	9.7164
2001	11.4273
2002	12.8201
2003	13.3547
2004	12.6387
2005	12.386
2006	11.2359
2007	11.5537
2008	14.3587
2009	20.1271
2010	20.8267
2011	18.7452
2012	17.6469
2013	17.0532
2014	14.5406
2015	12.776
2016	11.4449
2017	10.3213