Year	Percent
1961	13.44922
1962	14.23671
1963	15.38149
1964	15.70066
1965	17.89782
1966	20.33801
1967	19.85294
1968	18.53647
1969	18.46811
1970	22.1027
1971	24.46339
1972	28.26664
1973	36.1102
1974	34.86256
1975	28.48596
1976	25.11263
1977	26.08394
1978	25.41821
1979	29.08244
1980	26.84269
1981	23.23935
1982	23.23348
1983	27.88798
1984	23.56019
1985	26.23242
1986	28.3715
1987	31.68202
1988	34.16611
1989	29.54656
1990	30.41089
1991	34.42422
1992	39.749
1993	38.91229
1994	32.31109
1995	32.06451
1996	34.81096
1997	29.80253
1998	31.35476
1999	35.08643
2000	39.32907
2001	38.49062
2002	34.90541
2003	35.25167
2004	36.99063
2006	35.14376
2007	34.53929
2008	34.39007
2009	29.77228
2010	33.17248
2011	31.3353
2012	27.5737
2013	26.53968
2014	31.89218