Year	Percent
1970	23.84699
1971	23.97711
1972	23.29208
1973	26.74928
1974	34.67608
1975	27.3944
1976	27.31177
1977	25.21223
1978	22.07187
1979	23.82946
1980	21.61497
1981	25.52708
1982	26.28194
1983	26.66094
1984	28.7023
1985	26.73692
1986	25.10828
1987	22.65104
1988	20.94354
1989	23.23843
1990	20.4603
1991	17.53876
1992	18.67346
1993	21.25385
1994	22.64631
1995	23.65356
1996	23.14517
1997	22.92919
1998	20.81122
1999	23.23256
2000	22.03475
2001	22.95202
2002	22.7458
2003	24.12908
2004	25.28242
2005	25.42118
2006	23.74442
2007	24.75301
2008	22.67887
2009	19.65807
2010	20.08268
2011	20.44354
2012	20.92223
2013	22.01165
2014	22.93158
2015	23.38283
2016	24.38234