Year	Percent
1960	4.34192
1961	4.15279
1962	4.05939
1963	4.03379
1964	4.0107
1965	3.99199
1966	4.46281
1967	4.6606
1968	4.63041
1969	4.60171
1970	4.58468
1971	4.23453
1972	4.06512
1973	4.03825
1974	3.99905
1975	3.95069
1976	3.49369
1977	3.25562
1978	3.23131
1979	3.22683
1980	3.23369
1981	5.44381
1982	6.20189
1983	6.04085
1984	5.85139
1985	5.61724
1986	4.79053
1987	4.35927
1988	4.21861
1989	4.07939
1990	3.9656
1991	2.98688
1992	2.5424
1993	2.49348
1994	2.46663
1995	2.4511
1996	2.43862
1997	2.42092
1998	2.39884
1999	2.36253
2000	2.32143
2001	2.41412
2002	2.43716
2003	2.38422
2004	2.31665
2005	2.23831
2006	2.15371
2007	2.08246
2008	2.0659
2009	2.11191
2010	2.20304
2011	2.29703
2012	2.36628
2013	2.39038
2014	2.37716
2015	2.32609
2016	2.28099
2017	2.22389