Year	Percent
1975	27.59273
1976	19.66898
1977	20.19755
1978	29.50919
1979	31.16687
1980	30.0558
1981	29.56077
1982	31.22253
1983	29.3462
1984	23.93766
1985	26.38433
1986	24.13131
1987	22.17392
1988	23.16758
1989	20.44532
1990	18.4933
1991	16.73803
1992	17.72782
1993	18.0936
1994	20.83628
1995	27.07747
1996	26.41644
1997	17.92478
1998	20.92675
1999	19.86264
2000	20.77017
2001	24.50755
2002	25.0151
2003	21.13534
2004	20.97935
2005	22.44594
2006	21.11699
2007	21.73062
2008	20.81481
2009	24.54218
2010	30.08841
2011	36.07898
2012	33.37763