Annual % of total
1960 94.37437441752736
1961 94.327080864299
1962 94.43069422475692
1963 94.62430720183067
1964 94.7252776746792
1965 94.68512727807686
1966 94.58867052887035
1967 94.72457672863032
1968 94.7248890604034
1969 94.77968151418906
1970 94.6567912919222
1971 94.42032995288872
1972 94.11157949663021
1973 94.09435949551893
1974 93.39946619980435
1975 92.57874277884818
1976 92.59162623535273
1977 91.88540549278792
1978 91.20426394009455
1979 91.17403506785415
1980 90.53478658446795
1981 89.42133737582674
1982 88.53099942694408
1983 87.50957820759699
1984 86.48113110890726
1985 85.34984388456459
1986 84.67126619316811
1987 84.28843260806315
1988 83.97584858490815
1989 83.84360334646192
1990 83.8884753494929
1991 83.34238931791904
1992 83.09098246267578
1993 82.84818725306587
1994 82.7284262869155
1995 82.3809318275722
1996 82.26179146111458
1997 82.55210663497219
1998 82.27421132153314
1999 82.19224356037138
2000 82.1217873764684
2001 82.37188412410131
2002 82.36047136161302
2003 82.60721409014695
2004 82.20346184556671
2005 81.89351362806386
2006 81.52179968598625
2007 81.74777789146533
2008 81.21909380258406
2009 80.3324991135654
2010 80.21912560135246
2011 80.58865992718636
2012 80.64624889056313
2013 80.13653900155452
2014 79.66363017588768
2015 78.99552189517414