Year	Percent
1976	50.55293
1977	48.6014
1978	43.04384
1979	42.49164
1980	50.95301
1981	44.53813
1982	46.95837
1983	46.44751
1984	48.4663
1985	53.30237
1986	60.24942
1987	64.29516
1988	64.45397
1989	63.93468
1990	64.9569
1991	62.30529
1992	59.3046
1993	58.24254
1994	56.72276
1995	58.65759
1996	63.58557
1997	61.46211
1998	65.68374
1999	63.9352
2000	61.3857
2001	68.45676
2002	61.81901
2003	56.67804
2004	54.02084
2005	59.85487
2006	58.44394
2007	55.8675
2008	51.07052
2009	47.67717
2010	51.23767
2011	52.44415
2012	53.79217
2013	48.41741
2014	51.06284
2015	48.79493
2016	44.58386
2017	42.07163