Year	Percent
1977	32.03668
1978	45.02045
1979	39.75303
1980	40.24399
1981	42.07758
1982	44.25528
1983	47.18116
1984	52.92573
1985	56.5772
1986	57.74996
1987	51.88289
1988	62.02648
1989	53.63467
1990	54.15369
1991	44.48579
1992	49.63649
1993	41.73183
1994	38.78391
1995	43.13527
1996	45.02011
1997	42.65591
1998	42.13235
1999	45.34848
2000	45.2759
2001	40.91321
2002	38.60559
2003	35.87523
2004	35.35002
2005	36.4144
2006	34.70028
2007	32.55743
2008	30.2214
2009	28.4933
2010	26.89053
2011	27.03537
2012	27.51631
2013	25.22962
2014	25.63391
2015	36.90651
2016	37.34881
2017	34.52158