Annual % of total
1960 67.35579879267564
1961 69.29536272362768
1962 68.979503363447
1963 70.83497012005533
1964 71.45440443512217
1965 71.59104858258469
1966 70.4940189590892
1967 72.46605771092295
1968 73.1683342988945
1969 74.70312417556369
1970 78.36644683549312
1971 80.11409854643303
1972 80.42129493521655
1973 81.61574752364415
1974 81.90369111674644
1975 84.24607513869017
1976 85.37395232636999
1977 81.54773595758773
1978 81.25863103324987
1979 82.18049576424315
1980 84.32209903382827
1981 85.40409817597747
1982 85.28487465407048
1983 85.33380440652861
1984 84.55017051946894
1985 81.40423360480243
1986 84.21853762950956
1987 83.11159139066501
1988 82.13302383104161
1989 84.22662149777894
1990 80.44667749690223
1991 80.59660962361585
1992 83.56345603491293
1993 81.96160608149476
1994 80.82210984357947
1995 83.17811229319737
1996 80.55177441151767
1997 81.02220836467544
1998 83.49736503704405
1999 86.50723681452426
2000 84.03616853374484
2001 83.38537540083826
2002 85.2567327492204
2003 81.77346365857173
2004 82.75609099717434
2005 84.12212742186279
2006 80.8164495069197
2007 79.24051752370187
2008 78.63659452554116
2009 78.08765699434852
2010 75.12558464679661
2011 75.65654081341847
2012 75.81242013719098
2013 73.3496291275565
2014 72.81272629975807
2015 77.02412255583903