Year	Percent
1960	32.09266
1961	26.27472
1962	29.90118
1963	32.21279
1964	33.53716
1965	30.2292
1966	29.06867
1967	29.28098
1968	26.95732
1969	26.9388
1970	30.30978
1971	30.5262
1972	33.97
1973	28.28527
1974	27.26161
1975	32.70937
1976	33.72723
1977	37.27177
1978	39.69839
1979	39.68807
1980	40.95531
1981	38.57993
1982	39.4356
1983	40.14163
1984	41.13107
1985	39.68555
1986	37.80457
1987	36.7234
1988	35.8722
1989	34.69706
1990	37.27384
1991	35.44924
1992	36.17498
1993	34.19716
1994	35.17112
1995	34.10646
1996	34.93499
1997	36.58136
1998	33.56742
1999	33.28371
2000	35.19547
2001	35.85105
2002	38.36816
2003	38.28816
2004	36.53306
2005	35.66286
2006	29.84439
2007	34.0078
2008	34.46021
2009	37.80227
2010	36.07205
2011	32.81021
2012	34.60538
2013	33.43187
2014	37.3288
2015	38.61458
2016	37.29859
2017	35.43