Year	Percent
1977	65.29329
1978	59.56135
1979	63.67382
1980	60.41455
1981	63.12044
1982	59.79164
1983	57.66157
1984	50.84747
1985	54.85057
1986	61.30406
1987	56.27657
1988	52.88598
1989	47.50725
1990	47.46515
1991	47.87904
1992	40.94655
1993	44.54312
1994	43.67728
1995	42.66853
1996	46.8778
1997	49.9757
1998	52.70198
1999	49.37663
2000	55.1876
2001	48.99661
2002	43.90991
2003	50.09827
2004	44.23565
2005	51.16546
2006	46.41172
2007	52.52994
2008	47.68191
2009	40.32478
2010	44.48443
2011	47.11868
2012	46.9908
2013	48.09427
2014	41.30616
2015	40.5745
2016	35.98515
2017	37.53966