Year	Percent
1980	52.81674
1981	53.17059
1982	52.41262
1983	50.82125
1984	50.04897
1985	49.81336
1986	49.64457
1987	51.43559
1988	51.15056
1989	50.80051
1990	50.31436
1991	50.97515
1992	49.04908
1993	48.93075
1994	48.76601
1995	47.16514
1996	47.16618
1997	47.1652
1998	47.12758
1999	47.10747
2000	49.8638
2001	47.16577
2002	47.0949
2003	47.0946
2004	47.09913
2005	46.96231
2006	47.37655
2007	48.28294
2008	44.94385
2009	45.62101
2010	48.62171
2011	49.80312
2012	51.81579
2013	53.03904
2014	54.53156
2015	55.65417