Year	Percent
1970	44.18118
1971	44.18289
1972	44.18319
1973	44.17769
1974	44.17194
1975	44.19018
1976	44.19145
1977	44.1847
1978	44.15016
1979	44.14324
1980	44.28136
1981	44.19778
1982	44.151
1983	43.97743
1984	44.10863
1985	44.97195
1986	43.77987
1987	43.9171
1988	43.10957
1989	44.76466
1990	40.87545
1991	29.06494
1992	18.2286
1993	15.72162
1994	14.53618
1995	15.90691
1996	17.31162
1997	17.83081
1998	18.25202
1999	17.33145
2000	16.94596
2001	16.12662
2002	13.20224
2003	13.6352
2004	15.28964
2005	18.34403
2006	18.47456
2007	17.63125
2008	24.34962
2009	15.45425
2010	17.72168
2011	21.85679
2012	20.3552
2013	20.22347
2014	17.19027
2015	14.45059