Year	Percent
1960	3.88589
1961	3.44636
1962	3.51969
1963	3.61364
1964	3.59934
1965	3.47182
1966	3.72061
1967	4.43375
1968	4.85499
1969	5.24453
1970	6.94148
1971	7.39742
1972	8.10161
1973	9.37778
1974	7.73498
1975	11.0134
1976	12.87958
1977	13.98765
1978	14.95717
1979	18.74053
1980	22.9434
1981	19.15579
1982	17.2549
1983	20.24451
1984	21.59749
1985	20.92089
1986	21.83803
1987	18.70064
1988	17.35866
1989	17.54638
1990	16.15339
1991	17.64775
1992	17.86605
1993	17.89713
1994	17.29462
1995	17.26672
1996	17.80009
1997	17.91649
1998	16.71598
1999	17.15757
2000	17.76007
2001	16.99158
2002	16.98837
2003	17.12126
2004	17.7662
2005	15.35958
2006	11.2643
2007	13.18102
2008	14.23108
2009	15.05148
2010	15.61693
2011	16.09122
2012	21.06865
2013	21.628
2014	19.37616
2015	18.01154
2016	16.66058
2017	15.86182