Year	Percent
1970	23.98483
1971	23.50905
1972	24.55569
1973	26.29274
1974	28.4363
1975	22.86856
1976	24.88748
1977	27.35718
1978	28.45467
1979	32.3603
1980	27.26642
1981	27.80363
1982	27.21712
1983	23.34749
1984	22.30222
1985	19.5559
1986	18.359
1987	16.7177
1988	16.29636
1989	18.38795
1990	21.50137
1991	19.6492
1992	16.61703
1993	15.45069
1994	16.49423
1995	18.85043
1996	20.50631
1997	22.2372
1998	24.12937
1999	24.67763
2000	24.53379
2001	24.28259
2002	24.09024
2003	25.7478
2004	27.23862
2005	30.33083
2006	31.87956
2007	29.22847
2008	24.60493
2009	20.23477
2010	17.25749
2011	17.22506
2012	20.21884
2013	18.77023
2014	22.40157
2015	21.1849
2016	32.67628
2017	24.24729