Year	Percent
1971	24.89
1972	24.09
1973	22.45
1974	20.52
1975	20.63
1976	21.04
1977	21.26
1978	20.32
1979	21.52
1980	21.5
1981	21.41
1982	20.81
1983	21.81
1984	22.39
1985	23.32
1986	23.67
1987	24.41
1988	24.32
1989	23.14
1990	25.5
1991	26.6
1992	22
1993	21.03
1994	22.24
1995	22.7
1996	25.2
1997	24.72
1998	24.35
1999	24.31
2000	23.5
2001	25.06
2002	23.66
2003	23.67
2004	22.59
2005	22.5
2006	23.16
2007	22.38
2008	22.04
2009	23.34
2010	24.47