Year	Percent
1960	2.46526
1961	2.09768
1962	2.62855
1963	2.61604
1964	2.43003
1965	2.32592
1966	2.16537
1967	2.42682
1968	2.75456
1969	2.99137
1970	3.0653
1971	3.56098
1972	3.47425
1973	2.88224
1974	2.65544
1975	2.79523
1976	3.13142
1977	3.48177
1978	3.92371
1979	4.38092
1980	4.24445
1981	4.06316
1982	4.12037
1983	3.95336
1984	4.06444
1985	4.18912
1986	3.79533
1987	3.36139
1988	2.9335
1989	2.68467
1990	2.59425
1991	2.64502
1992	2.65742
1993	2.52482
1994	2.50238
1995	2.29084
1996	2.16439
1997	2.16367
1998	1.88651
1999	1.67728
2000	1.5327
2001	1.49286
2002	1.42894
2003	1.32348
2004	1.15465
2005	1.12371
2006	1.17838
2007	1.42552
2008	1.63933
2009	1.82004
2010	1.55607
2011	1.59496
2012	1.38234
2013	1.40544
2014	1.41714
2015	1.44829
2016	1.4444
2017	1.42258