Annual % of total
1960 26.59690429474602
1961 32.946145723336855
1962 39.599932191896926
1963 36.84891620834681
1964 39.8635477582846
1965 42.12076583210604
1966 43.5313262815297
1967 48.80770072194268
1968 51.24709683934162
1969 50.87404327695361
1970 51.51358789129687
1971 55.00499347007759
1972 57.07768775107238
1973 60.12205646652693
1974 60.06477927063341
1975 59.89060058048673
1976 59.57520891364902
1977 62.175769835918196
1978 63.589329789253846
1979 57.763221737020864
1980 59.5082522627172
1981 56.43650720778625
1982 55.0333024196948
1983 54.19788586934511
1984 51.167508804164754
1985 47.77678510068037
1986 46.021835979167975
1987 47.75306272229436
1988 46.65118304543475
1989 45.3648136449779
1990 44.05562562850165
1991 41.190644555694625
1992 42.12289728358807
1993 45.97003791042858
1994 45.00788085493406
1995 45.93666111969571
1996 43.727170665947696
1997 40.979326411488195
1998 38.94189424812999
1999 39.970623217711406
2000 37.79742221401533
2001 38.431376276671045
2002 38.275149433019415
2003 35.64265103121007
2004 34.43975868210152
2005 32.44922854346623
2006 29.07729173848098
2007 26.460976571962487
2008 25.95372876044568
2009 23.6508313935309
2010 23.7036894184168
2011 23.456011897268038
2012 23.39708343468742
2013 24.34716503755854
2014 23.319209135744483
2015 26.034771751187463
2016 26.531149790437546