Year	Percent
1977	42.6987
1978	44.2072
1979	40.85107
1980	47.43707
1981	43.23001
1982	35.39045
1983	34.31238
1984	40.19684
1985	40.72234
1986	46.17498
1987	49.13068
1988	45.34612
1989	42.79289
1990	39.46776
1991	46.19903
1992	49.16274
1993	46.22583
1994	43.57436
1995	39.54206
1996	40.03807
1997	39.29628
1998	39.76339
1999	37.47962
2000	35.7036
2001	33.19694
2002	31.76416
2003	35.49336
2004	38.59219
2005	41.72893
2006	37.0484
2007	34.57234
2008	31.86141
2009	24.41557
2010	30.09868
2011	34.69676
2012	37.94358
2013	41.21627
2014	64.00215
2015	60.481
2016	56.98581