Year	Percent
1977	82.65077
1978	82.66458
1979	68.87173
1980	70.38119
1981	67.3817
1982	65.78597
1983	66.56856
1984	63.58826
1985	64.7908
1986	63.818
1987	61.32277
1989	53.83148
1990	54.16077
1991	50.95109
1992	50.24702
1993	51.96669
1994	51.02148
1995	49.54914
1996	48.03768
1997	36.8804
1998	34.65716
1999	36.45689
2000	38.04756
2001	34.07259
2002	36.17545
2003	35.81023
2004	38.21523
2005	38.75989
2006	38.30928
2007	40.09195
2008	39.49363
2009	34.19068
2010	34.95329
2011	37.43527
2012	38.12695
2013	39.94975
2014	37.86608
2015	34.9813
2016	35.80853
2017	33.65455