Year	Percent
1960	13.70637
1961	14.42436
1962	16.30503
1963	12.41836
1964	11.74403
1965	10.33459
1966	12.52939
1967	12.2643
1968	13.90589
1969	15.97202
1970	14.79377
1971	15.99769
1972	21.73288
1973	13.3807
1974	26.8522
1975	26.87552
1976	33.69128
1977	38.14264
1978	29.45816
1979	28.08133
1980	29.55945
1981	24.91068
1982	25.39356
1983	25.32178
1984	25.4574
1985	25.52162
1986	23.85878
1987	19.52247
1988	14.99909
1989	17.12091
1990	16.54505
1991	17.97127
1992	23.17359
1993	25.97334
1994	29.95884
1995	27.2
1996	23.9
1997	21.1
1998	22.07488
1999	18.76541
2000	17.26788
2001	20.3448
2002	20.32119
2003	23.24424
2004	17.65631
2005	18.40693
2006	18.85441
2007	27.79913