Annual % of total
1960 31.555315345279176
1961 32.16483160621762
1962 33.62052312328556
1963 35.32358172117164
1964 36.683603082203305
1965 39.635625075785136
1966 39.08578394027123
1967 40.137868429264415
1968 41.602200915232075
1969 43.287621797185125
1970 46.24155405405405
1971 47.13647928568
1972 45.320977018185204
1973 48.01629852026593
1974 44.54278541338667
1975 44.343674422483524
1976 42.189111265441845
1977 41.5153290372974
1978 40.36667271737157
1979 38.89097509074978
1980 37.27864713113392
1981 37.222222222222214
1982 36.36306680241209
1983 34.20036180511416
1984 34.43583384996901
1985 29.834002188982122
1986 30.840935833371535
1987 29.836342549505307
1988 29.58927192304992
1989 29.34164147381484
1990 31.411555386949924
1991 29.682599448453022
1992 30.090552615889106
1993 32.16366683800852
1994 31.468273585244198
1995 30.008725303622715
1996 31.3259891852198
1997 29.153588356097405
1998 26.61109869987182
1999 26.768087016574587
2000 26.854462383046545
2001 23.36521915584416
2002 25.487878942446656
2003 27.140738089150258
2004 26.04356065376297
2005 26.90482990988065
2006 26.16939209726444
2007 25.699544852998418
2008 27.56149292149292
2009 27.208870743132042
2010 29.6389404930941
2011 30.955194805194804
2012 31.758423412914432
2013 32.53958525588631
2014 32.49619498215638
2015 31.167110407745298
2016 30.969322064798416