Annual % of total
1960 93.76106289961706
1961 93.62560708361822
1962 93.8137719087475
1963 94.19565521172737
1964 94.56969870151079
1965 94.60694039258378
1966 94.14087001402063
1967 94.360653470378
1968 94.5036046655083
1969 94.79038968631667
1970 94.22245621200553
1971 94.50827106402176
1972 93.98593856819514
1973 94.48097835125245
1974 94.26894850954068
1975 93.43752727375431
1976 93.90027924065562
1977 92.64788859849946
1978 92.4979578046907
1979 92.51077328825981
1980 91.78282081652107
1981 89.77261625613833
1982 89.0650840232683
1983 87.73915452001401
1984 85.78693341034746
1985 84.28127353475128
1986 83.58832258718235
1987 83.2213738436599
1988 82.28146015489828
1989 81.86885669516305
1990 80.88078633257244
1991 80.36281507952152
1992 79.7137439510754
1993 79.01289444250278
1994 78.88216124230229
1995 78.90350031621875
1996 78.71049398092532
1997 78.16503900016018
1998 78.27947760334911
1999 77.77490589079814
2000 77.36916220422293
2001 77.23596397750461
2002 77.0898352452003
2003 77.06382129746204
2004 76.67393906365079
2005 76.40953636931101
2006 76.12642814874452
2007 75.72293357523994
2008 74.83150619053478
2009 73.80373833091633
2010 73.18514518020581
2011 72.82949596336267
2012 71.86365252935241
2013 71.0335864186312
2014 69.67524016157651
2015 69.88602617063854