Year	Percent
1960	2.67913
1961	2.36407
1962	2.39868
1963	2.26084
1964	2.0145
1965	3.35209
1966	3.02198
1967	2.85697
1968	2.64974
1969	2.61559
1970	2.88729
1971	2.61905
1972	2.43581
1973	2.15465
1974	1.94135
1975	1.97214
1976	2.00275
1977	1.68773
1978	1.59967
1979	1.52193
1980	1.13843
1981	1.14315
1982	1.30353
1983	1.25458
1984	1.19954
1985	1.42952
1986	1.22039
1987	1.74399
1988	2.11807
1989	2.68625
1990	2.36384
1991	1.96333
1992	1.52153
1993	1.92792
1994	2.01601
1995	1.86214
1996	1.65484
1997	1.57769
1998	1.66229
1999	1.64547
2000	1.73073
2001	1.95188
2002	1.89577
2003	1.50348
2004	1.46127
2005	1.52401
2006	1.48108
2007	1.46629
2008	1.44192
2009	1.53863
2010	1.53941
2011	1.41185
2012	1.37866
2013	1.32945
2014	1.33024
2015	1.36443
2016	1.3485
2017	1.41003