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 94.15758517406512
1972 93.83968875450685
1973 94.19714101029844
1974 94.11100645370281
1975 93.87932226820604
1976 93.7962945186452
1977 93.78125504723937
1978 94.10004076740196
1979 94.07630005704603
1980 93.97684649265985
1981 93.16997835678055
1982 93.23252945848593
1983 93.2273671986631
1984 92.97035028709182
1985 92.95968732733252
1986 92.92992067612676
1987 93.07037635357351
1988 92.21663988436467
1989 92.66373953079204
1990 93.26899629494982
1991 93.1434904452662
1992 92.53043621004745
1993 91.87299822842219
1994 91.66273268979252
1995 91.33532679314395
1996 90.81706128957886
1997 90.47952165760718
1998 90.46900329497522
1999 90.1351115072162
2000 89.96115264316022
2001 89.9052741501404
2002 89.82742940609857
2003 90.13388127610632
2004 89.86812065662023
2005 89.78462827139023
2006 89.8525674246613
2007 89.88846972136196
2008 89.93664948376768
2009 89.08076391335088
2010 89.14323527269
2011 89.61960492433352
2012 89.38185917087756
2013 88.40710317362291
2014 89.32874706077632
2015 88.29755709217092