Year	Percent
1960	3.79158
1961	3.71801
1962	3.71154
1963	3.71947
1964	3.85118
1965	4.89658
1966	6.71235
1967	6.87651
1968	6.8146
1969	6.56156
1970	6.13808
1971	5.73019
1972	5.41319
1973	5.22846
1974	5.37945
1975	5.74039
1976	6.08882
1977	6.41454
1978	6.65301
1979	6.74069
1980	6.32775
1981	6.26074
1982	6.30289
1983	6.32333
1984	6.42161
1985	6.48799
1986	6.60903
1987	6.65328
1988	6.59676
1989	6.42105
1990	6.16935
1991	5.20323
1992	4.90671
1993	4.69267
1994	4.48253
1995	4.29857
1996	4.06646
1997	3.90968
1998	3.95226
1999	4.0826
2000	4.50027
2001	4.96864
2002	5.37221
2003	5.65942
2004	5.80526
2005	5.84769
2006	5.88761
2007	5.92063
2008	5.91942
2009	5.83257
2010	5.7525
2011	5.63898
2012	5.53239
2013	5.50536
2014	5.52058
2015	5.59334
2016	5.66961
2017	5.71534