Year	Percent
1971	60.95377
1972	62.81876
1973	64.60543
1974	64.57266
1975	65.26913
1976	63.97172
1977	64.23719
1978	65.09094
1979	65.36001
1980	69.05576
1981	71.68694
1982	75.9258
1983	76.80518
1984	76.47573
1985	78.39891
1986	79.59833
1987	79.19991
1988	79.08776
1989	79.22651
1990	78.95532
1991	81.47584
1992	85.00053
1993	84.1431
1996	80.33007
1997	80.12429
1999	80.2895
2000	81.9212
2001	83.28505
2002	89.94087
2003	87.84185
2004	87.97897
2005	89.77501
2006	93.62916
2007	95.64591
2008	93.43396
2009	93.44658
2010	92.26805
2011	93.64474
2012	95.03117
2013	95.08064
2014	96.01145
2015	94.99336
2016	91.9877