Year	Percent
1960	2.92793
1961	2.95095
1962	2.97677
1963	2.99475
1964	2.99356
1965	3.01548
1966	3.00808
1967	3.02072
1968	3.0957
1969	3.25099
1970	3.43663
1971	3.62794
1972	3.77011
1973	3.83684
1974	3.81964
1975	3.74632
1976	3.6519
1977	3.57229
1978	3.50155
1979	3.44591
1980	3.40052
1981	3.35663
1982	3.30523
1983	3.23444
1984	3.1369
1985	3.03373
1986	2.92467
1987	2.83738
1988	2.78486
1989	2.77141
1990	2.79228
1991	2.81811
1992	2.82789
1993	2.83941
1994	2.83721
1995	2.82325
1996	2.81179
1997	2.79649
1998	2.77623
1999	2.75081
2000	2.71982
2001	2.68863
2002	2.65615
2003	2.60935
2004	2.55347
2005	2.49116
2006	2.42562
2007	2.36432
2008	2.31348
2009	2.27376
2010	2.24386
2011	2.21556
2012	2.1844
2013	2.14924
2014	2.10558
2015	2.05994
2016	2.01152
2017	1.96973