Annual % of total
1960 94.13454680133336
1961 94.09571954319732
1962 94.21763356720116
1963 94.42413857295968
1964 94.53739930247939
1965 94.52379554232209
1966 94.43048498457715
1967 94.56634525412176
1968 94.56557653806482
1969 94.63801786260352
1970 94.54807463236827
1971 94.10380572113877
1972 93.81867404796564
1973 93.84281226142556
1974 93.17677008009404
1975 92.38051128085422
1976 92.42109056011745
1977 91.76886536293615
1978 91.15522835068587
1979 91.10874013895743
1980 90.5200389299574
1981 89.46395414757853
1982 88.63824589379855
1983 87.66297739083629
1984 86.7177986258281
1985 85.68500776308059
1986 84.98240712000509
1987 84.62463670138332
1988 84.31593958890416
1989 84.20775310537259
1990 83.53234741218229
1991 83.00683120839128
1992 82.86645791621875
1993 82.68605773156068
1994 82.64126690074367
1995 82.29607638760275
1996 82.32527573606127
1997 82.67672581217559
1998 82.4410231662649
1999 82.33440919310529
2000 82.3107717057543
2001 82.57116384455566
2002 82.54052142973026
2003 82.76916033821068
2004 82.38486464930753
2005 82.14809474710648
2006 81.84983694619933
2007 82.06535961973951
2008 81.55278410335892
2009 80.7800899591913
2010 80.61930746862132
2011 80.99242272844697
2012 81.03145232980582
2013 80.52744996446667
2014 80.16115894205397
2015 79.6762980161753