Annual % of total
1960 28.444017563117452
1961 28.63247863247863
1962 29.16762342135476
1963 28.716839829122936
1964 29.080646801586497
1965 28.335196571641514
1966 28.836520451278474
1967 28.729501671708324
1968 29.858721909084252
1969 30.406936644004332
1970 27.259960311402835
1971 26.23419012647899
1972 26.77226406734603
1973 27.573296906225497
1974 27.687486334815247
1975 27.133429759537155
1976 25.103338299166992
1977 25.083247687564235
1978 25.906804342070426
1979 27.5631195062652
1980 27.233391771420045
1981 29.6389510890686
1982 28.914737394170974
1983 33.08772443046769
1984 35.28819141722367
1985 36.46175327370844
1986 35.19573341073178
1987 35.526634173320886
1988 38.523050409306336
1989 39.058513279791775
1990 27.73350634304582
1991 26.97838530692513
1992 33.267568854671005
1993 31.193190241414488
1994 33.085522634459984
1995 31.995508986995773
1996 30.619967728922948
1997 30.04534561805678
1998 28.09558808733273
1999 31.300311111111114
2000 32.816514401440145
2001 33.61903729678036
2002 35.02437546746447
2003 34.62705179682794
2004 35.86631551741962
2005 36.314054900323555
2006 38.482374166161314
2007 41.16439444214019
2008 38.51486188425586
2009 36.884044957774464
2010 35.435049032258064
2011 38.399758189398455
2012 36.52642481341001
2013 31.333218997361477
2014 31.457837837837836
2015 32.04726611796982
2016 29.20094883328648