Annual % of total
1960 27.32897085068412
1961 30.003452641270577
1962 32.54380272550292
1963 33.376288659793815
1964 37.44821092278719
1965 38.66909928941809
1966 41.97646179712311
1967 46.07762180016515
1968 49.42419257078535
1969 50.1230718739744
1970 48.92216435185185
1971 53.293960486535894
1972 53.90890107021665
1973 55.76278417748522
1974 51.09111791730475
1975 53.11804759657521
1976 54.65787821720025
1977 55.912856304220206
1978 55.4797142128094
1979 56.14097755551586
1980 49.88782950084128
1981 53.4722675899915
1982 53.23349217154526
1983 50.860609480812634
1984 46.77332616294703
1985 46.33639471743648
1986 51.42392188771359
1987 53.7499206198006
1988 51.42307163481369
1989 51.43650901206125
1990 47.44381843143985
1991 48.219698814482534
1992 50.39184151205133
1993 52.21985640138409
1994 50.85611254074455
1995 49.101118012422354
1996 49.97064406779661
1997 49.272100591715976
1998 52.55825421370033
1999 50.76221411578112
2000 49.4262883677003
2001 49.57010749521425
2002 49.85893613954159
2003 49.82904378189632
2004 48.986862796833776
2005 49.48814664218258
2006 49.393153846153844
2007 50.243665075800116
2008 48.827662943588294
2009 50.63328935113319
2010 48.30627787307032
2011 46.93459206093452
2012 47.62425433881124
2013 48.131117870722434
2014 49.1693886110663
2015 48.93978780680918
2016 49.39661303044644