Annual % of total
1960 59.82356647763075
1961 56.86531014027225
1962 52.63625221980441
1963 47.80299698948009
1964 44.62326635165889
1965 42.87298367989082
1966 40.641244048399074
1967 37.08006467453141
1968 35.601937254339596
1969 33.82547550690831
1970 29.844510159305543
1971 25.898883637099296
1972 23.480880210728056
1973 23.429985544214283
1974 25.044742774092033
1975 24.549144227486714
1976 22.94561445977568
1977 21.886799851000845
1978 19.347889586680296
1979 19.99693016116654
1980 23.69033106944525
1981 26.630533399603955
1982 26.974951830443157
1983 26.020952183383468
1984 27.6972103473024
1985 29.715059427715314
1986 28.15106524473788
1987 27.66805940177169
1988 28.181666512188336
1989 27.04222834054421
1990 26.543930035879036
1991 26.91364280158457
1992 26.06839378238342
1993 26.41742939278698
1994 26.98647634443737
1995 27.750997024190177
1996 28.28452315318277
1997 29.477746062572933
1998 28.74765922651934
1999 30.04550249165873
2000 31.046202375417387
2001 31.990629580905843
2002 32.41775412810592
2003 33.1311269308592
2004 36.3351196855725
2005 34.56886597683347
2006 35.73434904978744
2007 36.19127703121433
2008 37.41059726462117
2009 35.166517013103764
2010 37.96002223029548
2011 33.803969822714635
2012 33.95303125648847
2013 36.70344476167816
2014 36.670901854371955
2015 37.87329741853576
2016 37.0312561145306