Annual % of total
1960 94.02150650561848
1961 93.95176934840252
1962 94.14510041765017
1963 94.50935993934391
1964 95.00374686109103
1965 95.02813063001868
1966 94.34535818257164
1967 94.7014071935444
1968 94.93965044798296
1969 95.17184392898996
1970 94.33540762970964
1971 94.18444638219202
1972 93.52201812476535
1973 94.32892069368542
1974 94.11210288178418
1975 93.22477450131943
1976 93.88719320189762
1977 92.56546160300681
1978 92.42799043801136
1979 92.04647759070674
1980 91.23984580580539
1981 89.07712431454709
1982 88.01324583918964
1983 86.52584899564164
1984 84.33698768744391
1985 82.5424083658352
1986 81.80502828327865
1987 81.48562737514942
1988 80.53126380185142
1989 80.17596519611061
1990 79.56676722767658
1991 79.33162428792248
1992 78.54812658166023
1993 77.85387055600297
1994 78.01743193205056
1995 78.06609718217663
1996 77.74822462820381
1997 77.37886920632009
1998 77.80392056047717
1999 77.3487095763229
2000 76.83885377178625
2001 76.77614419180378
2002 76.60436832292616
2003 76.4432863318021
2004 76.3220432715407
2005 76.11145752881069
2006 75.5805138031328
2007 75.21275897011013
2008 74.3904873323779
2009 73.4728205894215
2010 72.7811999660712
2011 72.33455766169584
2012 71.69580201759442
2013 70.84715101678735
2014 69.41660493849797
2015 69.95485442857749