Annual % of total
1960 74.68165699548678
1961 72.25054337087532
1962 69.91441491946033
1963 67.44202170069678
1964 62.77547843927979
1965 58.694442512346114
1966 55.35726734053677
1967 52.96164869660161
1968 49.35510810058458
1969 45.246358755302424
1970 39.03727705286511
1971 33.27600253462478
1972 32.22623952465035
1973 32.60278313221198
1974 35.86440677966101
1975 31.54037901312431
1976 31.76510407852429
1977 30.704600764862672
1978 32.155581947743464
1979 33.617488625071914
1980 34.88088462476624
1981 37.29044085035924
1982 38.84954924041551
1983 36.074327981237595
1984 39.879647987756094
1985 38.999648999649
1986 35.08234119911599
1987 35.380512091038405
1988 33.03613841487923
1989 37.314451458795425
1990 34.9926603238496
1991 31.749990347490343
1992 29.938624588266716
1993 27.644870583961495
1994 28.480685813751087
1995 27.39127694859038
1996 25.363544579321896
1997 25.02513717421125
1998 24.785492839795662
1999 22.36835079213921
2000 24.801026603001365
2001 22.5213418962312
2002 20.99634551195309
2003 18.966803463203462
2004 18.44113138045957
2005 16.868001084892867
2006 16.541156925908883
2007 15.34256812314753
2008 15.226297577854671
2009 11.353829637804754
2010 13.043044049967126
2011 13.513836978131213
2012 12.376511162594777
2013 12.829375841010245
2014 13.092361357586512
2015 12.060269957983195
2016 11.193058736217134