Year	Percent
1970	26.37468
1971	26.2227
1972	25.91469
1973	25.25322
1974	25.11431
1975	24.89143
1976	23.82163
1977	23.49924
1978	22.77718
1979	22.04502
1980	23.28023
1981	22.15663
1982	22.21664
1983	22.30376
1984	22.6284
1985	22.81465
1986	22.65644
1987	22.82587
1988	22.56802
1989	22.72512
1990	22.63286
1991	22.40006
1992	22.49554
1993	21.62772
1994	21.62338
1995	22.0925
1996	22.2882
1997	22.45271
1998	22.32603
1999	22.63836
2000	23.65266
2001	22.89071
2002	22.65572
2003	22.16299
2004	22.12967
2005	22.23951
2006	22.8196
2007	22.16667
2008	22.59394
2009	19.95014
2010	19.70489
2011	20.25471
2012	20.39792
2013	20.0618
2014	19.78498
2015	19.67236
2016	20.33793
2017	19.85721