Year	Percent
1980	54.82999
1981	53.99847
1982	51.97502
1983	54.72832
1984	53.44072
1985	51.90553
1986	50.9879
1987	50.10156
1988	52.50659
1989	53.87205
1990	54.02031
1991	53.34907
1992	53.14837
1993	52.65484
1994	53.87317
1995	51.60556
1996	51.65044
1997	52.52522
1998	52.97306
1999	52.29989
2000	52.49284
2001	52.28516
2002	53.77367
2003	53.11291
2004	54.17223
2005	53.83034
2006	54.98539
2007	55.6121
2008	55.85328
2009	54.39581
2010	53.88499
2011	55.02578
2012	54.95365
2013	55.65545
2014	55.21825
2015	54.17404
2016	54.22238
2017	53.7641