Year	Percent
1971	65.79716
1972	59.94834
1974	54.51917
1975	55.96938
1976	58.37998
1977	60.44685
1978	61.72892
1979	61.76359
1980	62.97475
1981	66.60704
1991	65.60938
1992	67.71114
1999	68.6393
2000	71.6884
2001	68.02154
2002	69.58222
2003	70.48984
2004	69.27864
2005	74.89932
2006	70.96721
2007	76.11506
2008	81.34766
2009	82.40569
2011	89.00289
2012	95.0658
2013	96.15721
2014	95.08159
2015	100.2383
2017	95.20428