Year	Percent
1980	43.86607
1981	40.48472
1982	37.82288
1983	35.52555
1984	34.69575
1985	36.03339
1986	37.13787
1987	36.33136
1988	37.80414
1989	39.77415
1990	38.85119
1991	39.26647
1992	36.94209
1993	37.25846
1994	33.72173
1995	32.88866
1996	33.95004
1997	33.67586
1998	36.24733
1999	35.80679
2000	35.83354
2001	35.1927
2002	33.96425
2003	34.32055
2004	35.91395
2005	38.08498
2006	37.60039
2007	34.3599
2008	35.44499
2009	37.02235
2010	36.43011
2011	38.07491
2012	36.45237
2013	36.33003
2014	37.22506
2015	37.575
2016	37.40504
2017	39.25155