Annual % of total
1960 4.845252403846154
1961 7.8813498602851615
1962 9.519907122857338
1963 11.648850490554986
1964 11.614134368625386
1965 12.321684420357565
1966 12.440469276338714
1967 12.532169631867518
1968 13.24380274961516
1969 11.783952959028833
1970 12.436840705611205
1971 12.402078007751298
1972 13.841210444968683
1973 15.09433962264151
1974 15.628117565804619
1975 16.57524721878863
1976 16.51477289431133
1977 16.786727788692428
1978 16.01643444087174
1979 16.28738944648713
1980 18.008295956564258
1981 20.09199698134905
1982 22.496808963267622
1983 24.982573539662624
1984 25.64976419153843
1985 28.662559690883242
1986 29.73714768288821
1987 31.95405965863774
1988 34.794421300489034
1989 38.12909085214995
1990 43.31790665064103
1991 44.93223984048614
1992 45.032194690265484
1993 36.7822921732865
1994 37.5302838063439
1995 46.77752921535893
1996 45.50429440581543
1997 48.346105874960735
1998 46.30492753623188
1999 50.43183918324764
2000 52.68237207186718
2001 51.94353807960279
2002 53.34896569336852
2003 53.853705983172325
2004 58.49879661614382
2005 56.06510183160196
2006 54.024348329793405
2007 53.320864755851616
2008 53.63873446327684
2009 55.93665650406504
2010 51.74234269061496
2011 52.27429933431118
2012 53.46963759592225
2013 49.3669875
2014 53.74434772942027
2015 52.85611317104627
2016 55.496506945951815