Annual % of total
1960 85.44074708887621
1961 86.6094140073205
1962 87.40390522825355
1963 87.86942422229343
1964 89.08839987206701
1965 87.97762182751164
1966 87.48781591414595
1967 87.74547222489501
1968 88.49453945252145
1969 89.511758479888
1970 88.99204257987063
1971 90.19969369309229
1972 90.12373159462952
1973 89.77446241105375
1974 88.65248261131772
1975 88.39898888918214
1976 89.59968424417724
1977 88.1923619073637
1978 87.60895289985788
1979 87.0076277971248
1980 85.89521616401274
1981 83.96376022136376
1982 82.74158705788483
1983 82.44589222455637
1984 81.8351143304607
1985 81.04281229177755
1986 79.74839655694737
1987 79.5788581060508
1988 74.69315383406521
1989 76.54434927780457
1990 79.1323454283578
1991 79.12700715650539
1992 77.23721117428765
1993 77.0111424905957
1994 77.58570757509024
1995 77.98279868095946
1996 78.19818694350876
1997 78.41612404994794
1998 78.5155637093458
1999 76.60732844589133
2000 76.53529223461383
2001 76.89638903354617
2002 77.31087416751208
2003 78.14442930483148
2004 77.69929365819102
2005 77.03042942998188
2006 74.69833424034242
2007 72.62977853771083
2008 71.55486310268553
2009 69.83650771641395
2010 70.26705703172875
2011 69.15418339945117
2012 67.30250678634732
2013 66.25380350853943
2014 64.81315646614684
2015 65.66182198947268