Annual % of total
1960 34.65973534971645
1961 38.07167743857422
1962 41.55974087691654
1963 46.474760116812675
1964 49.68516231745026
1965 51.97983206020055
1966 53.92914864805836
1967 57.747469908377745
1968 59.41999700155789
1969 61.53384622286022
1970 65.44119049890298
1971 69.36439041436007
1972 71.69953204965688
1973 71.15009590472796
1974 69.41996548700557
1975 69.70931972301715
1976 70.99653029936255
1977 71.5607661693493
1978 72.13743245216882
1979 71.12816577129702
1980 66.60977922253825
1981 63.57877131113268
1982 63.01392741774513
1983 63.36355149880718
1984 60.47718975255093
1985 57.889044229282426
1986 59.08202264296073
1987 59.253186286417595
1988 59.18509593104088
1989 60.03218078449601
1990 60.33989831222084
1991 58.77262476710743
1992 60.748480138169256
1993 59.395512589441815
1994 59.77833705952156
1995 58.93514576352118
1996 58.48225563339319
1997 57.52366323392874
1998 57.987385281767956
1999 56.79385336524029
2000 55.89977961874973
2001 54.37755462917087
2002 52.99326478702867
2003 52.69581972067314
2004 51.79350989604406
2005 51.47400726631626
2006 50.17239519096668
2007 47.61065877882514
2008 47.86180973077387
2009 45.95563080611328
2010 44.23313992111272
2011 43.44422564491779
2012 42.88786994298127
2013 40.617063526052824
2014 39.86466880359397
2015 38.88882209056285
2016 37.78663826735759