Annual % of total
1960 91.76526065381225
1961 92.10454800251851
1962 92.75396860184433
1963 91.04656541746809
1964 92.40352139560173
1965 92.82543251017957
1966 91.59480865932696
1967 93.64900655768504
1968 94.01785496114256
1969 92.4590134889005
1970 93.39177997872987
1971 92.50995477698093
1972 90.75550334306295
1973 92.18236470769821
1974 92.08240220872506
1975 92.72735644223296
1976 93.93108019586106
1977 91.59255098510663
1978 91.67016715310231
1979 91.40037469402806
1980 94.03165878065462
1981 93.34953373346153
1982 93.07060361320075
1983 92.00145714409199
1984 86.58322286717105
1985 85.40211513023198
1986 82.8923545525935
1987 81.85179412086868
1988 79.3042298683435
1989 77.60440170780001
1990 77.38649913588938
1991 77.9523570058137
1992 79.25417767178493
1993 77.69169530341983
1994 78.59018687112915
1995 79.60094520888593
1996 77.85351034423455
1997 80.06129404745712
1998 79.52609681435756
1999 80.97590440887573
2000 80.63494268797741
2001 79.8499960208187
2002 81.46071287465873
2003 80.82302301864463
2004 81.83202563415655
2005 83.4668123985147
2006 82.5095887666763
2007 83.18621647779008
2008 81.80831581898948
2009 79.71021291685348
2010 76.00086331064998
2011 76.50008868696364
2012 75.00814839911963
2013 72.55135062662742
2014 71.53112184817807
2015 72.95554611833776