Year	Percent
1960	7.8342
1961	7.80767
1962	7.80825
1963	7.86485
1964	7.96639
1965	8.12732
1966	8.26771
1967	8.40545
1968	8.47319
1969	8.47812
1970	8.43922
1971	8.3965
1972	8.37622
1973	8.31283
1974	8.31125
1975	8.31372
1976	8.32162
1977	8.27993
1978	8.22268
1979	8.07653
1980	7.91024
1981	7.65241
1982	7.43649
1983	7.36767
1984	7.52896
1985	7.74369
1986	8.11694
1987	8.3245
1988	8.03471
1989	7.16362
1990	5.9547
1991	4.60992
1992	3.48508
1993	2.91704
1994	3.19267
1995	4.10427
1996	5.22967
1997	6.11772
1998	6.76806
1999	7.012
2000	6.96419
2001	6.87637
2002	6.84316
2003	6.74581
2004	6.5867
2005	6.24004
2006	4.73024
2007	4.52642
2008	4.35141
2009	4.21068
2010	4.10454
2011	4.0038
2012	3.8533
2013	3.69659
2014	3.53967
2015	3.38319
2016	3.23019
2017	3.0835