Year	Percent
1981	58.03
1982	58.25
1983	58.18
1984	57.54
1985	57.23
1986	56.38
1987	54.75
1988	56.68
1989	55.74
1990	49.8
1991	49.88
1992	46.15
1993	47.17
1994	50.43
1995	48.83
1996	47.78
1997	47.11
1998	39.64
1999	43.32
2000	38.98
2001	40.63
2002	39.36
2003	39.13
2004	37.04
2005	35.55
2006	34.87
2007	31.98
2008	31.32
2009	32.52
2010	31.52