Year	Percent
1971	54.67
1972	48.75
1973	32.38
1974	9.706
1975	5.742
1976	7.04
1977	13.32
1978	5.889
1979	5.506
1980	2.837
1981	2.597
1982	2.452
1983	8.722
1984	7.522
1985	10.72
1986	8.85
1987	11.98
1988	3.094
1989	14.25
1990	7.561
1991	8.219
1992	7.255
1993	3.967
1994	4.307
1995	4.476
1996	10.99
1997	14.62
1998	9.296
1999	15.42
2000	9.968
2001	9.737
2002	14.09
2003	14.47
2004	14.74
2005	14.17
2006	13.19
2007	13.35