Year	Percent
1971	8.884
1972	8.168
1973	7.937
1974	7.281
1975	7.827
1976	8.462
1977	7.251
1978	6.502
1979	6.474
1980	6.762
1981	8.016
1982	5.393
1983	5.345
1984	5.523
1985	5.021
1986	5.159
1987	4.512
1988	4.869
1989	3.869
1990	3.813
1991	3.832
1992	4.052
1993	3.448
1994	3.059
1995	3.191
1996	2.562
1997	2.466
1998	2.225
1999	2.587
2000	3.646
2001	3.347
2002	3.515
2003	3.415
2004	3.072
2005	2.436
2006	2.548
2007	2.572
2008	2.746
2009	3.161
2010	2.373