Annual % of total
1960 25.16536007108015
1961 26.444836634356
1962 28.184871276754976
1963 28.78863214089446
1964 29.03716614548624
1965 29.209732260390346
1966 29.586147566489114
1967 30.850965132013116
1968 31.994878422118134
1969 32.911526922856844
1970 34.094823298266554
1971 34.234482273824305
1972 35.33349383975429
1973 36.432074932647666
1974 37.609004806369406
1975 37.82793797323294
1976 37.324273719662266
1977 37.39247183257377
1978 38.78268853498557
1979 38.66470867611816
1980 38.086089522262924
1981 39.29421438230107
1982 38.75996524052652
1983 38.234026639705135
1984 37.06969304342648
1985 34.705225489720085
1986 34.64686760668214
1987 30.653679682562984
1988 29.621849324541966
1989 29.878339955095434
1990 51.45033720269577
1991 52.15793861082834
1992 29.083223248879293
1993 29.3911119832692
1994 24.93829192681369
1995 24.223430123330562
1996 23.129120100626963
1997 23.514837287850547
1998 23.29103770858154
1999 22.236200460117434
2000 22.389503054716346
2001 22.442178755207877
2002 21.706470852438795
2003 21.63669482784672
2004 21.309483612755194
2005 21.664727504327665
2006 21.78166959102944
2007 21.326760120891482
2008 22.942334515293155
2009 24.00324310947919
2010 21.700284810126583
2011 23.900883630805524
2012 24.077295933671692
2013 22.827471274984298
2014 24.50873952926826
2015 23.221374676571234
2016 25.56288719054151