Year	Percent
1973	53.28563
1974	53.66738
1976	61.9757
1977	65.56374
1978	65.38921
1979	67.89149
1980	70.43238
1981	74.17107
1983	70.91701
1984	68.99597
1985	57.18514
1986	59.52746
1987	57.67849
1988	58.88279
1989	53.70481
1990	51.67125
1991	57.60873
1992	51.54129
1993	52.84413
1994	51.82608
1995	50.12961
1996	51.75375
1997	48.74084
1998	47.46041
2000	52.82475
2001	59.23071
2006	54.437
2007	53.22571
2009	53.61262
2011	59.34969
2012	62.92491
2013	60.63687
2014	62.72334
2015	68.244
2016	71.78511