Annual % of total
1960 46.295336787564764
1961 46.78508881661246
1962 46.69854280510018
1963 48.38581897405426
1964 47.64014640724331
1965 48.99944923811272
1966 51.65073065127187
1967 51.6913139554649
1968 53.216721019863634
1969 48.57099189974018
1970 51.032092813017925
1971 49.57889718735103
1972 69.17450365726228
1973 64.4122383252818
1974 60.50354051927616
1975 68.75
1976 65.174456879526
1977 61.51419558359621
1978 62.3400365630713
1979 63.320463320463325
1980 62.93807009121459
1981 61.16504854368932
1982 54.71215351812367
1983 51.64737310774711
1984 48.231511254019296
1985 47.29487638839125
1986 46.193218170185546
1987 44.94590417310664
1988 44.34217650243639
1989 42.89997274461707
1990 46.37863715277778
1991 48.65631578947369
1992 45.51175126903553
1993 43.613086714399365
1994 43.549010339734124
1995 40.65827794561933
1996 42.62178953626635
1997 44.363547706905635
1998 42.899137662337665
1999 44.05505718547986
2000 35.535177829099304
2001 38.30578355314197
2002 36.0550455705432
2003 34.492598672720916
2004 34.8202849656076
2005 32.4323784775298
2006 30.44937883008356
2007 26.795451434588053
2008 23.846964886964887
2009 22.34616536312849
2010 21.452457493080267
2011 24.6420782800441
2012 25.67974995688912
2013 23.06251238032354
2014 24.760871473354232
2015 20.50635095550286
2016 20.950733658801195