Annual % of total
1960 100
1961 100
1962 100
1963 92.0245398773006
1964 93.80733944954129
1965 92.23880597014926
1966 82.48587570621469
1967 88.6861313868613
1968 53.156146179402
1969 53.31412103746397
1970 73.97454031117398
1971 66.58624849215921
1972 41.03585657370518
1973 43.625498007968126
1974 29.850746268656714
1975 30.592734225621417
1976 36.36363636363637
1977 39.175257731958766
1978 35.78847969782814
1979 32.687105500450855
1980 29.009762900976295
1981 33.72043010752688
1982 36.824450242266124
1983 20.23172905525847
1984 26.00557546794106
1985 19.10071942446043
1986 14.785214785214784
1987 21.33461661854347
1988 20.3798613204703
1989 14.058106841611998
1990 17.61798882681564
1991 17.96298550724638
1992 6.873757131214344
1993 15.375026778882939
1994 18.04701570680628
1995 12.295553914327916
1996 14.569661256175017
1997 18.919889042995838
1998 19.36346228239845
1999 13.599941747572814
2000 16.48764483627204
2001 12.797583892617448
2002 18.95255516840883
2003 20.86678173719376
2004 23.703586168432793
2005 25.97015458937198
2006 16.607435555555554
2007 25.0522555410691
2008 26.48471134436819
2009 14.857800242620298
2010 15.850812163202463
2011 14.961021897810218
2012 9.274459917199849
2013 15.848682197496524
2014 7.753848444738584
2015 13.014254901960784
2016 12.591652317880794