Year	Percent
1960	1.94507
1961	1.90415
1962	1.88388
1963	1.92548
1964	2.04453
1965	2.20143
1966	2.40268
1967	2.54603
1968	2.51026
1969	2.25174
1970	1.86509
1971	1.43042
1972	1.09672
1973	0.96716
1974	1.11421
1975	1.45156
1976	1.83958
1977	2.15685
1978	2.39377
1979	2.51157
1980	2.5464
1981	2.55117
1982	2.57573
1983	2.6269
1984	2.71777
1985	2.82061
1986	2.9236
1987	2.97441
1988	2.92839
1989	2.76646
1990	2.53189
1991	2.31146
1992	2.1261
1993	1.92892
1994	1.7214
1995	1.52874
1996	1.31724
1997	1.16818
1998	1.20757
1999	1.48556
2000	1.92071
2001	2.39463
2002	2.79381
2003	3.08968
2004	3.24512
2005	3.29815
2006	3.33901
2007	3.38472
2008	3.37692
2009	3.31462
2010	3.22118
2011	3.10605
2012	3.00844
2013	2.9651
2014	2.99226
2015	3.0611
2016	3.13533
2017	3.18076