Year	Percent
1977	66.14306
1978	67.51562
1979	60.20354
1980	62.87726
1981	62.36944
1982	59.55142
1983	58.01593
1984	58.3068
1985	59.27091
1986	57.90495
1987	55.80324
1989	57.16884
1990	55.95925
1991	55.16753
1992	51.21454
1993	51.39327
1994	53.38048
1995	54.9163
1996	57.81906
1997	42.85448
1998	43.06901
1999	39.24585
2000	41.59738
2001	38.42829
2002	34.10253
2003	35.25331
2004	37.78675
2005	42.63638
2006	49.24144
2007	47.92086
2008	47.93559
2009	42.33036
2010	43.72232
2011	50.89842
2012	46.12378
2013	45.56532
2014	49.84622
2015	38.70577
2016	37.67781
2017	41.80939