Annual % of total
1960 25.753284033230045
1961 23.499641198020925
1962 22.71858407079646
1963 22.091367031439987
1964 21.85076099862758
1965 21.50284309875951
1966 20.29356448944384
1967 20.348882587090568
1968 19.973180632067265
1969 19.24751577616338
1970 17.237232077659893
1971 15.859479809062263
1972 16.321425478895872
1973 13.640949754489812
1974 12.448987267974347
1975 15.443851452420084
1976 14.812433996051242
1977 15.946417020053188
1978 16.726916837130563
1979 17.21234643683691
1980 18.328631350778927
1981 19.478437358757667
1982 21.339285714285715
1983 22.902646926873036
1984 24.20106668045252
1985 23.655540303383088
1986 22.85191790619144
1987 22.977131684094193
1988 23.35104971576061
1989 23.09318009118541
1990 22.396417732391676
1991 23.73830358656431
1992 23.870792723004698
1993 22.1045455190688
1994 21.945008659587074
1995 21.88942024471635
1996 21.69829043958891
1997 22.32936555701837
1998 23.423870285150795
1999 22.980775134305446
2000 23.725846019417478
2001 23.907763640667536
2002 22.161668411136695
2003 21.0609091242482
2004 20.587073801768266
2005 20.61966561812463
2006 21.364119430018295
2007 20.042663702718315
2008 20.43576045074518
2009 16.946496927803377
2010 16.25520793226548
2011 14.17002391733002
2012 13.804364330884233
2013 12.427000629100386
2014 13.347480554616165
2015 12.646818897637797
2016 11.964646671995348