Year	Percent
1963	2.51149
1964	3.49645
1965	3.41864
1966	3.51259
1967	3.0191
1968	2.61473
1969	2.38687
1970	2.13054
1971	2.08759
1972	1.79584
1973	1.68816
1974	1.95767
1975	2.13109
1976	2.70172
1977	2.24195
1978	2.37523
1979	2.1387
1980	2.10206
1981	1.81805
1982	2.0631
1983	1.95121
1984	1.75512
1985	1.64371
1986	1.78721
1987	1.85638
1988	1.7497
1989	1.54012
1990	1.46107
1991	1.21083
1992	2.14013
1993	2.50563
1994	3.14643
1995	2.93503
1996	3.09409
1997	3.6374
1998	3.96567
1999	3.75508
2000	3.43339
2001	3.8207
2002	3.70083
2003	3.25121
2004	3.28388
2005	2.83418
2006	2.64381
2007	2.92332
2008	3.02475
2009	3.84851
2010	3.51801
2011	4.32571
2012	4.46108
2013	4.8445
2014	5.54848
2015	6.27421
2016	6.42447
2017	5.70824