Year	Percent
1965	36.04334
1966	33.76289
1967	33.99503
1968	29.068
1969	30.68567
1970	34.4368
1971	31.90869
1972	30.49281
1973	29.6143
1974	37.64728
1975	36.5979
1976	37.19741
1977	37.38981
1978	35.56378
1979	36.76178
1980	37.58908
1981	38.98306
1982	42.63926
1983	42.49795
1984	40.0897
1985	33.51632
1986	33.79288
1987	34.77309
1988	31.87061
1989	30.62362
1990	27.89596
1991	30.6884
1992	30.05301
1993	29.94756
1994	31.25825
1995	30.56554
1996	30.64227
1997	28.73892
1998	27.66615
1999	31.59843
2000	31.60797
2001	30.81298
2002	30.74674
2003	28.00945
2004	28.51038
2005	29.24686
2006	29.10727
2007	29.54594
2008	29.16271
2009	29.60426
2010	29.68297
2011	29.93158
2012	30.35306
2013	34.56657
2014	39.66239
2015	38.90505
2016	38.81455
2017	39.3122