Annual % of total
1960 21.826280623608017
1961 18.951669719599828
1962 22.59607718067294
1963 23.595686463866087
1964 23.43212706729982
1965 24.55072033268974
1966 25.971786833855802
1967 24.947745595700212
1968 22.88980459922903
1969 14.979134636503405
1970 6.428498310983724
1971 6.960120391271632
1972 4.611219223284542
1973 6.403462944995895
1974 6.388153659060018
1975 9.472682794237564
1976 9.136212624584719
1977 8.042704626334519
1978 8.385384134915677
1979 7.770022750935102
1980 12.844320643763544
1981 13.388738375924433
1982 14.732997042963996
1983 13.014464398015512
1984 21.75661098944203
1985 22.347568352286476
1986 18.798758998765024
1987 21.9117821899893
1988 17.699286923226325
1989 19.07041859162817
1990 29.798866139604023
1991 26.897526569451312
1992 30.668830378561818
1993 31.112561462152254
1994 30.649885746204237
1995 29.001619098905046
1996 33.71581925963835
1997 31.865485698761987
1998 18.40661560848587
1999 30.00870174558228
2000 17.357944819216904
2001 20.280698075075374
2002 19.542716134091354
2003 18.69965530607985
2004 18.048615806037997
2005 15.823254065040649
2006 15.784919252952486
2007 15.033561240065266
2008 16.003628771408877
2009 16.37410454003904
2010 17.69823979469468
2011 16.98790450817966
2012 16.461760041088855
2013 14.264591257263604
2014 12.747137026833997
2015 19.218056393121994
2016 18.437235645884684