Year	Percent
1980	53.77341
1981	51.93831
1982	57.91059
1983	60.31978
1984	59.95346
1985	62.53141
1986	64.00978
1987	61.464
1988	60.9692
1989	59.39231
1990	51.27493
1991	39.75387
1992	39.05229
1993	32.68919
1994	29.94673
1995	25.20054
1996	19.19116
1997	21.58384
1998	21.96499
1999	22.30739
2000	22.67489
2001	23.77722
2002	23.88628
2003	24.09054
2004	22.9221
2005	24.18322
2006	25.23483
2007	26.15161
2008	24.92004
2009	26.38496
2010	23.80921
2011	25.61467
2012	24.99979
2013	23.75514
2014	23.56134
2015	24.08805
2016	24.42667
2017	24.51549