Annual % of total
1960 72.12772797481357
1961 69.75669076459042
1962 69.21717560361763
1963 69.71001924883554
1964 68.1674166149277
1965 69.59110062973795
1966 68.76136156104687
1967 66.24079800331194
1968 65.51641274571057
1969 57.043839001919274
1970 54.346032039575576
1971 53.1285150843177
1972 50.17854951994119
1973 51.613895168549675
1974 51.93912149896559
1975 47.66505956526852
1976 45.07610232482532
1977 45.55306905628098
1978 44.445323546576525
1979 42.55074363711407
1980 39.59806602427958
1981 33.82147341478727
1982 29.8067730937455
1983 28.457697898724852
1984 30.653190835902876
1985 29.266406955060248
1986 31.010731967898714
1987 31.873471006187927
1988 30.3177079391172
1989 30.161399872283106
1990 28.639913794964357
1991 27.838666068833923
1992 29.7638545885607
1993 30.045656181786345
1994 29.982114220599737
1995 29.289170954562042
1996 30.736419072580258
1997 29.75087974082556
1998 28.025357081133293
1999 24.467962464225263
2000 22.622225912864995
2001 22.891121892831496
2002 23.085975813297114
2003 22.873787595210082
2004 24.0894510485188
2005 23.659011958993165
2006 19.713460115676867
2007 16.151274105087932
2008 13.167049866738841
2009 12.170354326513015
2010 11.51979150601258
2011 10.254952587195088
2012 10.330714298599672
2013 10.40420686553414
2014 10.928487267979623
2015 11.288868750735006