Year	Percent
1971	4.497
1972	7.704
1973	8.033
1974	8.042
1975	8.039
1976	8.511
1977	8.779
1978	8.623
1979	8.327
1980	8.718
1981	8.39
1982	8.832
1983	9.501
1984	9.202
1985	13.4
1986	17.12
1987	16.94
1988	18.11
1989	18.39
1990	18.94
1991	18.78
1992	20.34
1993	18.45
1994	18.36
1995	17.84
1996	18.19
1997	19.13
1998	20.05
1999	19.12
2000	20.26
2001	20.38
2002	21.21
2003	22.93
2004	22.32
2005	22.64
2006	23.06
2007	22.51
2008	22.8
2009	23.9
2010	22.91