Year	Percent
1973	10.39732
1974	11.87524
1975	10.84211
1976	10.892
1977	11.02185
1978	11.53617
1979	12.2716
1980	13.33018
1981	13.53434
1982	12.67865
1983	12.78833
1984	13.2684
1985	12.32959
1986	13.47302
1988	13.17122
1989	13.70805
1997	12.74247
1998	12.82909
1999	13.16532
2000	10.08899
2001	10.04261
2002	10.31131
2003	10.78384
2004	10.28455
2005	9.60441
2006	10.38527
2007	9.23474
2008	9.49356
2009	8.94309
2010	9.97542
2011	9.18868