Year	Percent
1971	0.7943
1972	1.876
1973	2.406
1974	3.189
1975	3.214
1976	3.676
1977	3.321
1978	3.805
1979	4.408
1980	4.289
1981	3.895
1982	4.568
1983	6.168
1984	4.912
1985	4.772
1986	4.374
1987	4.146
1988	4.872
1989	4.183
1990	4.523
1991	3.826
1992	4.353
1993	4.816
1994	4.789
1995	4.717
1996	4.261
1997	4.655
1998	4.696
1999	4.882
2000	5.047
2001	5.745
2002	4.817
2003	5.318
2004	5.868
2005	6.296
2006	6.762
2007	6.294
2008	6.99
2009	6.696
2010	6.351