Annual % of total
1960 55.55001247193814
1961 53.14810340661995
1962 50.73904627837409
1963 47.744995578422696
1964 39.39279224712296
1965 35.09815368897321
1966 31.343970000353767
1967 27.867445054945055
1968 24.07156235871601
1969 20.86747445347844
1970 13.258926264661811
1971 9.28495197438634
1972 6.560386697961936
1973 6.242805277605598
1974 6.9045115875119984
1975 5.569268374511731
1976 5.441618222289456
1977 5.962186655952142
1978 6.461115053000493
1979 6.24402054005506
1980 7.158055653108021
1981 8.929841721500978
1982 9.565929565929567
1983 14.661963238999547
1984 17.430543266678463
1985 17.087195756704503
1986 16.129195309340883
1987 16.7379704850262
1988 19.2991214057508
1989 18.773326138765235
1990 20.148107178968655
1991 17.840036900369004
1992 18.14119404932794
1993 17.46267707082833
1994 19.19922119171643
1995 20.06429597176585
1996 18.25698769549218
1997 17.579485223450263
1998 17.41012161514498
1999 15.86673966839891
2000 15.65987492298213
2001 14.720573476702508
2002 17.00612298507463
2003 17.375547929132935
2004 16.79075336895911
2005 16.68346371375841
2006 16.568810091014598
2007 16.153243029824456
2008 16.12779369974001
2009 15.461519247539554
2010 14.787119654124794
2011 17.25361931138667
2012 19.152113382427626
2013 18.87646130346232
2014 22.189398892521183
2015 25.690569223958004
2016 23.906050420168068