Annual % of total
1960 60.49762483322269
1961 58.65194273794734
1962 56.5696002468376
1963 58.187424452072555
1964 56.85607662659121
1965 56.89427222622877
1966 59.01729394955597
1967 58.20607970228454
1968 57.77258009102303
1969 60.79059758636076
1970 63.01105148180631
1971 61.06634511490176
1972 60.82285047598505
1973 59.273300910849315
1974 57.17783656781723
1975 57.856347808592766
1976 56.74258262878568
1977 58.95527015915481
1978 59.755902965105776
1979 57.17117537441621
1980 57.84799390809562
1981 54.84309783455138
1982 54.062938277424834
1983 52.95456054817104
1984 52.90660572094087
1985 52.15408157406895
1986 55.48632704886024
1987 53.79633919425145
1988 51.78077123808406
1989 53.37572015413918
1990 52.0530053123507
1991 52.94426708066512
1992 53.59213645053023
1993 54.758248152746894
1994 53.372501535781105
1995 53.03900925557243
1996 52.457211036702176
1997 54.566814486099915
1998 54.03449738837062
1999 55.195822266288275
2000 54.344018853171114
2001 55.656292067344815
2002 53.53006357273661
2003 58.88828460209561
2004 55.891555972885484
2005 54.98216280325153
2006 56.68576091744204
2007 56.18881465161404
2008 61.670896904400195
2009 63.11011116181548
2010 63.04306399544679
2011 57.32151682512342
2012 57.80716859421601
2013 61.84011850701244
2014 57.9782333483243
2015 56.951628649981146