Year	Percent
1971	72.55569
1972	66.18117
1974	60.59802
1975	63.04011
1976	66.31035
1977	68.59588
1978	70.56139
1979	70.27338
1980	70.82943
1981	75.74477
1991	73.42457
1992	75.52532
1999	72.95357
2000	75.97664
2001	71.54208
2002	73.04234
2003	69.58806
2004	74.46031
2005	77.7297
2006	72.72496
2007	78.61126
2008	83.61349
2009	86.10453
2011	91.68168
2012	85.19227
2013	97.21653
2014	96.02325
2015	100.60907
2017	95.32185