Annual % of total
1960 89.33975945488103
1961 89.61421351964283
1962 90.24593900972727
1963 90.48215583075728
1964 90.86472001675193
1965 91.11421493492654
1966 91.26485868739802
1967 91.43384413892046
1968 91.72587447833783
1969 92.1627322655627
1970 92.61986407562019
1971 58.550548884245565
1972 59.301829803831545
1973 60.42576353563648
1974 60.87894259129959
1975 62.150387416510924
1976 62.99207080736011
1977 64.3640929950993
1978 65.69862741424517
1979 66.0432604069311
1980 66.08994435714519
1981 65.84130400263558
1982 66.43728456329143
1983 66.44879199978509
1984 66.82741013906833
1985 67.17153432937887
1986 67.63386034352544
1987 68.28452694689302
1988 68.74368769924644
1989 68.91048089833602
1990 77.61569834979281
1991 77.2016120448625
1992 76.60944011908613
1993 76.44456755143433
1994 75.94062142351116
1995 76.36655133881207
1996 76.40090017890209
1997 76.32929967539928
1998 76.12345522026301
1999 76.2170071122191
2000 76.27889906201382
2001 76.50362350338284
2002 76.7853124024198
2003 77.62910919922929
2004 78.37299622024065
2005 78.92780643724409
2006 79.4630272336375
2007 79.84503241203626
2008 80.02918161966237
2009 80.06400295201742
2010 80.62783612874328
2011 80.9960334230629
2012 80.87730478112191
2013 80.64154593947805
2014 80.84743149946114
2015 88.08939589093121