Annual % of total
1960 94.62158342052608
1961 93.97716023193324
1962 93.36332577884518
1963 93.26608938370285
1964 92.47639446137138
1965 91.32575869945711
1966 90.67715438423359
1967 89.80864695150409
1968 88.57556517812077
1969 87.98826173826174
1970 85.96034785960349
1971 85.57063086054107
1972 85.21655052845664
1973 83.71971242486063
1974 83.36363828572637
1975 82.61892673019841
1976 82.0608722821592
1977 81.65556712669228
1978 81.50021642633442
1979 81.16236284681936
1980 82.05555248596981
1981 82.11580594679185
1982 82.90225642272752
1983 83.11583444036363
1984 84.45623880193367
1985 85.0713005148111
1986 84.5618150200186
1987 84.89397413772724
1988 84.729359721754
1989 84.05527481655821
1990 87.8176451944492
1991 85.9231191877826
1992 85.78902554096165
1993 84.57912795767687
1994 79.03342899190582
1995 80.67292147058825
1996 78.96042159180456
1997 79.13050401880277
1998 77.6449043685814
1999 76.44469027121497
2000 74.10884109431537
2001 74.58897820163487
2002 74.50923280423281
2003 73.12320725562647
2004 70.95988834404612
2005 70.07273768043804
2006 70.99916297876405
2007 68.88160576953761
2008 69.22366405033732
2009 67.2978261454619
2010 68.05935169248423
2011 68.22303615699154
2012 64.94343431679577
2013 69.2468447692153
2014 66.98236088752012
2015 64.98474589171424
2016 63.85502935877761