Year	Percent
1970	30.18866
1971	34.31195
1972	35.63016
1973	40.72648
1974	39.24843
1975	25.94671
1976	27.93534
1977	32.60218
1978	36.05311
1979	41.52645
1980	41.84189
1981	35.71856
1982	41.2852
1983	32.25372
1984	51.28141
1985	57.70953
1986	31.83511
1987	38.95615
1988	51.16819
1989	46.18952
1990	37.03451
1991	37.79112
1992	50.11189
1993	32.71686
1994	34.30937
1995	35.14326
1996	31.83577
1997	39.88313
1998	35.84284
1999	42.81647
2000	33.11749
2001	26.82298
2002	23.35128
2003	24.59181
2004	26.38522
2005	25.16865
2006	27.60053
2007	33.95079
2008	32.79144
2009	35.22254
2010	35.22432
2011	30.947
2012	25.69778
2013	25.8232
2014	31.38561
2015	32.23849
2016	31.30411
2017	31.59359