Year	Percent
1971	34.31174
1972	34.12066
1978	38.25438
1979	40.28311
1980	37.54751
1981	39.91579
1982	40.68897
1983	41.8535
1984	42.47841
1985	43.61133
1986	46.47554
1988	52.72449
1989	53.87165
1990	52.05156
1992	47.72585
1994	46.20388
1996	47.10007
1997	47.03381
1998	49.18863
2000	44.52835
2001	49.14978
2002	50.84201
2003	50.22931
2004	50.40557
2005	55.24886
2006	50.53019
2007	51.59698
2008	57.52704
2009	56.99759
2010	55.63385
2011	58.5736
2012	56.90063
2013	56.81999
2014	56.53946
2015	54.84393
2016	54.34293