Year	Percent
1960	2.44481
1961	2.58223
1962	2.72919
1963	2.86137
1964	2.97478
1965	3.05302
1966	3.28979
1967	4.10308
1968	4.142
1969	4.13206
1970	4.10651
1971	4.06986
1972	4.04545
1973	4.01945
1974	4.01322
1975	3.94022
1976	3.50673
1977	3.5051
1978	3.55213
1979	3.65388
1980	3.77977
1981	3.90909
1982	4.00399
1983	4.0201
1984	4.05398
1985	4.23428
1986	4.05984
1987	3.89716
1988	3.77517
1989	3.69482
1990	3.65027
1991	3.60905
1992	3.5427
1993	3.42378
1994	3.11493
1995	2.38812
1996	2.18881
1997	2.00623
1998	1.8466
1999	1.71301
2000	1.60418
2001	1.4946
2002	1.40017
2003	1.35576
2004	1.34446
2005	1.28465
2006	1.36174
2007	1.42895
2008	1.48591
2009	1.52143
2010	1.5386
2011	1.55646
2012	1.57412
2013	1.57915
2014	1.57707
2015	1.5758
2016	1.56812
2017	1.55602