Year	Percent
1972	21.17119
1973	22.0144
1974	20.666
1975	18.87472
1976	17.73264
1977	18.35483
1978	19.15855
1980	19.69424
1981	19.23404
1982	18.51097
1983	17.86284
1984	16.84152
1985	17.67667
1986	17.18032
1987	16.55215
1988	17.59891
1989	17.89701
1990	42.43433
1991	43.05083
1992	44.17204
1993	45.26292
1994	42.31401
1995	51.11118
1996	45.41983
1997	47.7331
1998	43.65176
1999	47.5967
2000	45.91493
2001	48.53346
2002	51.21401
2003	53.98873
2004	55.34449
2005	59.01567
2006	60.21604
2007	62.85861
2008	26.13145
2009	26.52748
2010	26.13968
2011	26.12809
2012	26.3967
2013	26.7607
2014	26.85874
2015	25.61881
2016	26.24297