Year	Percent
1960	9.98532
1961	9.9723
1962	10.70984
1963	11.69528
1964	10.93439
1965	11.34884
1966	12.82455
1967	12.62411
1968	13.39683
1969	13.35616
1970	14.70738
1971	13.7732
1972	16.81079
1973	15.46703
1974	17.89028
1975	18.70928
1976	20.32313
1977	20.66648
1978	15.14634
1979	14.50272
1980	18.16426
1981	17.86989
1982	16.95259
1983	16.28529
1984	16.18031
1985	16.51323
1986	18.84756
1987	25.6665
1988	25.1426
1989	23.47259
1990	24.54927
1991	22.71204
1992	23.36227
1993	26.61561
1994	21.32053
1995	25.47356
1996	24.55131
1997	25.11079
1998	23.85661
1999	21.34168
2000	23.80016
2001	18.13547
2002	21.24316
2003	22.47351
2004	25.20531
2005	27.03355
2006	29.56524
2007	28.71373
2008	28.9359
2009	23.01844
2010	26.97276
2011	31.26869
2012	28.30415
2013	29.77321
2014	29.03338
2015	28.36202
2016	28.22664
2017	30.86184