Year	Percent
1960	2.36955
1961	2.41514
1962	2.3637
1963	2.44663
1964	2.64824
1965	2.95229
1966	3.45138
1967	3.79376
1968	3.83727
1969	3.38592
1970	2.96604
1971	2.76315
1972	2.68562
1973	2.37935
1974	2.2628
1975	2.26732
1976	2.21661
1977	2.2472
1978	2.21569
1979	2.19273
1980	2.24896
1981	2.2966
1982	2.39327
1983	2.51981
1984	2.50523
1985	2.52327
1986	2.54043
1987	2.37299
1988	2.16181
1989	2.05183
1990	2.07591
1991	2.16804
1992	2.16875
1993	2.17803
1994	2.1166
1995	2.02131
1996	1.93044
1997	1.86733
1998	1.87112
1999	1.88924
2000	1.82984
2001	1.87009
2002	1.87396
2003	1.84629
2004	1.82741
2005	1.80185
2006	1.82184
2007	1.8146
2008	1.79724
2009	1.92918
2010	1.8624
2011	1.76939
2012	1.67992
2013	1.64953
2014	1.78129
2015	1.95845
2016	2.09285
2017	1.98929