Annual % of total
1960 94.13454680133341
1961 94.09571954319732
1962 94.21763356720112
1963 94.42413857295968
1964 94.53739930247941
1965 94.52379554232209
1966 94.43048498457715
1967 94.56634525412177
1968 94.56557653806483
1969 94.6380178626035
1970 94.54807463236828
1971 84.45071747939836
1972 84.33545928495718
1973 84.77311851172902
1974 84.1496830170751
1975 83.40228818641089
1976 83.80503982254298
1977 83.45717019694254
1978 83.27090605395131
1979 83.34838381867806
1980 82.69029401525748
1981 81.67315369405239
1982 80.98839022910686
1983 80.31095870498316
1984 79.76756585558564
1985 79.05676152464946
1986 78.75818184161187
1987 78.71931253380326
1988 78.74699658260548
1989 78.72607376098044
1990 80.76166867089796
1991 80.30420835396099
1992 80.08244068463495
1993 79.98313226153245
1994 79.7929832022258
1995 79.81737201141544
1996 79.83418787798777
1997 79.97706842880524
1998 79.75976102679348
1999 79.72722449825017
2000 79.78384868253987
2001 80.03830701139174
2002 80.05704119833653
2003 80.55352270507805
2004 80.65153868945382
2005 80.72447731597298
2006 80.8357144829528
2007 81.19416166100714
2008 81.05485545582646
2009 80.61346858226932
2010 80.7781258315195
2011 81.23056229508738
2012 81.16535015062586
2013 80.9427289687651
2014 80.91140771928029
2015 79.67629801617531