Year	Percent
1980	56.90527
1981	47.62549
1982	46.84914
1983	45.08658
1984	46.16009
1985	40.98124
1986	43.03366
1987	34.6317
1988	36.67585
1989	38.96104
1990	41.13288
1991	34.55869
1992	38.5142
1993	31.25755
1994	31.22389
1995	29.84119
1996	23.63294
1997	23.04943
1998	21.5284
1999	22.95128
2000	22.15378
2001	20.54078
2002	20.39506
2003	21.13925
2004	23.6582
2005	21.24016
2006	20.70443
2007	20.25486
2008	19.36193
2009	18.81844
2010	17.17634
2011	16.45699
2012	16.45136
2013	18.37196