Year	Percent
1970	26.8666
1971	26.12418
1972	26.21413
1973	26.32535
1974	27.43136
1975	28.83927
1976	28.46537
1977	28.27197
1978	29.60334
1979	32.09981
1980	34.16845
1981	34.05276
1982	34.22593
1983	35.02247
1984	36.55442
1985	35.69653
1986	29.08442
1987	28.5724
1988	27.46836
1989	29.20149
1990	29.53005
1991	28.40675
1992	28.02127
1993	27.59586
1994	27.90047
1995	28.79349
1996	30.96922
1997	31.47345
1998	27.59974
1999	29.56496
2000	36.48021
2001	35.1993
2002	33.25249
2003	33.41027
2004	35.01653
2005	37.98663
2006	39.68181
2007	37.16437
2008	40.26829
2009	34.2634
2010	34.73796
2011	36.98586
2012	36.78915
2013	35.58908
2014	33.96844
2015	30.94128
2016	28.2922
2017	29.89538