Year	Percent
1973	58.06126
1974	56.9288
1975	59.03357
1976	60.32612
1977	60.79428
1978	72.23054
1979	60.69325
1980	57.87089
1981	57.74914
1982	56.22374
1983	56.02829
1984	57.7169
1985	59.07699
1986	59.31109
1987	60.86074
1988	61.34621
1990	59.0498
1991	59.78727
1999	53.75282
2000	54.02395
2003	62.32561
2004	65.17272
2006	56.24766
2007	60.56178
2008	77.71143
2009	77.40946
2010	79.29022
2011	78.12875
2012	81.60419
2014	79.24748
2015	80.22415
2016	79.373