Annual % of total
1960 67.36429038587313
1961 61.22492080253432
1962 55.04322766570605
1963 57.21449369136202
1964 54.56697298802562
1965 51.82755388940956
1966 50.35452749041032
1967 44.88077007219427
1968 42.27001918610522
1969 41.68950203156005
1970 41.03027175782594
1971 37.11300606898671
1972 35.12630217198883
1973 32.375785969670815
1974 32.647552783109404
1975 31.993748604599244
1976 32.073219259848784
1977 29.368397392672513
1978 26.452439719005127
1979 33.139252789907815
1980 31.958762886597935
1981 34.13368836654118
1982 35.831717393137176
1983 38.30140537037788
1984 40.56806002143623
1985 43.89045426431173
1986 44.71983434774424
1987 42.75108677242703
1988 42.56931339817099
1989 42.18519688355443
1990 47.316468898146816
1991 47.91424280350437
1992 44.682919975972766
1993 39.9805024738161
1994 40.52924770999805
1995 38.48323190300725
1996 39.596481531410085
1997 42.32610930316649
1998 44.0418333763219
1999 40.493475397936436
2000 40.26217708429508
2001 36.85911618970574
2002 36.52904285988853
2003 37.56516563241467
2004 38.23247506678539
2005 37.26917790732309
2006 39.26550959439274
2007 39.43259092639374
2008 39.914375696378826
2009 41.50361637077442
2010 41.29324380721594
2011 41.14237347349868
2012 40.52788737533447
2013 39.71613288493573
2014 40.76501761390324
2015 37.82353167041156
2016 39.5363274513468