Annual % of total
1960 31.781808955981223
1961 30.833803297429345
1962 30.850618510002835
1963 31.668590748887286
1964 32.24926175615316
1965 32.1892306045227
1966 31.82719005737476
1967 31.496017677602055
1968 29.768476866828735
1969 28.795536276409745
1970 27.005606931960358
1971 25.43889329367344
1972 24.66096970456448
1973 25.39820301281322
1974 26.035969151982542
1975 26.148098770240434
1976 27.64879920890554
1977 27.210677100449647
1978 27.979081537019685
1979 28.885520807461784
1980 30.937143593593632
1981 32.8421147944417
1982 33.399831922899104
1983 34.963823043289885
1984 35.47086355576386
1985 36.238002303427145
1986 35.363693018490544
1987 35.88000603817975
1988 35.98032984461147
1989 36.29056667724936
1990 36.77671786732274
1991 36.72781060670661
1992 36.636111696241954
1993 36.607518693691446
1994 36.316544114893276
1995 35.89295562620687
1996 36.15768571920706
1997 35.38463090236284
1998 35.31357665408625
1999 35.41204441830205
2000 35.8520935840773
2001 35.450802626429535
2002 36.830598731534316
2003 36.34364158081006
2004 36.66565584151999
2005 36.89271809981793
2006 37.02272456148415
2007 36.77636355084342
2008 37.360511311550255
2009 35.70114527429718
2010 35.44897447926614
2011 35.35906575665591
2012 32.848111009431925
2013 32.468819078494946
2014 32.342900042723485
2015 29.15700635587693
2016 27.071413869706095