Annual % of total
1960 31.25686059275521
1961 29.763313609467453
1962 28.30654420206659
1963 27.873002478772218
1964 25.78053493338757
1965 25.66610769517421
1966 24.86387594197848
1967 24.832829167330043
1968 24.771246614449893
1969 24.984399119781912
1970 28.33765837276751
1971 28.565600046628198
1972 28.53622064687638
1973 29.306114188864434
1974 26.1496975439108
1975 26.17971433737118
1976 27.45546486497828
1977 29.465570400822198
1978 30.78596013464957
1979 30.706938470170194
1980 29.69898168525495
1981 25.87116235172197
1982 25.814789840413578
1983 23.181701832010823
1984 24.67306015693113
1985 25.106607796520624
1986 26.488408373544246
1987 28.96920045628954
1988 26.435157259801812
1989 26.73767488055893
1990 32.11359902682037
1991 30.926630144683244
1992 27.82775378998333
1993 32.998012580754846
1994 30.60984360066035
1995 33.085919821088375
1996 31.87730939895119
1997 33.857189208252514
1998 34.15375691719489
1999 33.2346
2000 30.559708595859586
2001 33.9814121772394
2002 32.49716636392777
2003 29.955878337683195
2004 28.09483820944898
2005 27.419254775075668
2006 28.953511218920557
2007 29.323832434674408
2008 27.86550257325911
2009 29.50632513661202
2010 30.70343612903226
2011 28.069257891602145
2012 28.243931236999874
2013 30.737414248021107
2014 30.548918918918922
2015 32.600585733882035
2016 33.52052431824571