Year	Percent
1960	5.06762
1961	5.34738
1962	5.63662
1963	5.61092
1964	5.53594
1965	5.42084
1966	5.32226
1967	5.25944
1968	5.26971
1969	5.35885
1970	5.53893
1971	6.61637
1972	7.52103
1973	7.61387
1974	7.6872
1975	7.70888
1976	7.72147
1977	7.70763
1978	7.75737
1979	7.84257
1980	7.9413
1981	8.0435
1982	8.10305
1983	8.02442
1984	7.79653
1985	7.46335
1986	7.11003
1987	6.81761
1988	6.6575
1989	6.64646
1990	6.74708
1991	6.88346
1992	6.96363
1993	6.91263
1994	6.73652
1995	5.72551
1996	5.48515
1997	5.29908
1998	5.23051
1999	5.29006
2000	5.43749
2001	5.58772
2002	5.70013
2003	5.75813
2004	5.75341
2005	5.6928
2006	4.92122
2007	4.89453
2008	4.87256
2009	4.84885
2010	4.83088
2011	4.80882
2012	4.77466
2013	4.72272
2014	4.65432
2015	4.56136
2016	4.4695
2017	4.38339