Year	Percent
1960	21.357
1961	17.59909
1962	20.93376
1963	19.42764
1964	16.70843
1965	17.04007
1966	17.65772
1967	15.7516
1968	17.36444
1969	17.11029
1970	17.88503
1971	17.72846
1972	18.53955
1973	22.54186
1974	24.61317
1975	21.87699
1976	19.95641
1977	18.56877
1978	15.17114
1979	19.55685
1980	18.62805
1981	15.98795
1982	14.22139
1983	13.54569
1984	12.69668
1985	12.58084
1986	11.51136
1987	16.00718
1988	17.14551
1989	24.75452
1990	28.3392
1991	24.40526
1992	26.25649
1993	27.86528
1994	33.06198
1995	31.03971
1996	31.82598
1997	32.42074
1998	30.52917
1999	32.31676
2000	35.38948
2001	35.3782
2002	38.07201
2003	33.47053
2004	40.05439
2005	40.38786
2006	39.50457
2007	38.64345