Year	Percent
1973	16.49
1975	9.21
1977	11.75
1979	16.02
1986	15.29
1989	14.24
1991	15.16
1992	15.26
1993	12.14
1994	12.86
1995	14.21
1996	14.73
1997	14.6
1998	15.23
1999	16.65
2001	16.97
2002	16.62
2003	15.8
2004	16.05
2005	17.77
2006	18.36
2007	17.92
2008	16.18
2009	16
2011	12.91