Year	Percent
1960	1.32727
1961	1.07067
1962	0.94877
1963	1.17177
1964	1.8404
1965	2.76263
1966	3.75614
1967	4.48697
1968	4.754
1969	4.47872
1970	3.88515
1971	3.26172
1972	2.79362
1973	2.45074
1974	2.28668
1975	2.25826
1976	2.21589
1977	2.1719
1978	2.27302
1979	2.54365
1980	2.90839
1981	3.29696
1982	3.59826
1983	3.74278
1984	3.6978
1985	3.52775
1986	3.35609
1987	3.2193
1988	3.05715
1989	2.87418
1990	2.69153
1991	2.4862
1992	2.31835
1993	2.27918
1994	2.39946
1995	2.61656
1996	2.86482
1997	3.05221
1998	3.13633
1999	3.08673
2000	2.9537
2001	2.8052
2002	2.69627
2003	2.62969
2004	2.62137
2005	2.65075
2006	2.68262
2007	2.69709
2008	2.70448
2009	2.70065
2010	2.68814
2011	2.67543
2012	2.66214
2013	2.63949
2014	2.60621
2015	2.5659
2016	2.52386
2017	2.48415