Year	Percent
1970	26.52335
1971	30.36484
1972	31.08041
1973	34.30779
1977	38.67927
1978	38.05131
1979	33.7937
1980	38.83301
1982	35.22344
1983	34.29113
1984	33.28167
1985	36.47879
1986	44.23716
1987	54.60993
1988	56.03913
1993	54.52084
1994	59.67691
1995	54.7397
1999	70.18552
2000	70.17913
2001	72.34421
2002	80.24691
2003	79.90941
2004	81.21756
2005	85.19051
2006	85.06205
2007	85.97835
2008	85.35874
2010	89.32009