Annual % of total
1960 10.592557848655408
1961 9.517066626919064
1962 10.564774977805094
1963 9.751434034416826
1964 10.884177869700103
1965 12.321196358907672
1966 13.018932481751824
1967 12.281868040551768
1968 11.03111826836546
1969 11.177314834949767
1970 9.503695881731785
1971 8.760584515345315
1972 8.202135505178438
1973 6.807297289815353
1974 6.656271567700213
1975 7.323581495766926
1976 7.43069178227884
1977 9.246174617461746
1978 10.016995523130493
1979 9.811901238414206
1980 10.69188553508428
1981 11.489370784598309
1982 12.527421038059336
1983 14.370282344138552
1984 17.191640961028803
1985 19.25465838509317
1986 17.674607271922707
1987 19.403116938191324
1988 19.01425718989736
1989 18.67214940460893
1990 18.03166700292545
1991 20.000680865581437
1992 18.90264161794307
1993 18.795121758527745
1994 18.90961521192529
1995 18.386626501035195
1996 17.837046785850134
1997 16.93663955099286
1998 16.029567340762142
1999 16.039313086288338
2000 16.391080692103497
2001 15.84833427212417
2002 15.388964006555724
2003 16.932092451915306
2004 16.67297680254621
2005 15.980091676499955
2006 15.650463500808431
2007 15.744774408284023
2008 15.048928149183146
2009 12.68288857851381
2010 14.719446609508962
2011 15.382903241273493
2012 13.933073977333096
2013 14.256842770161123
2014 14.536162240025257
2015 15.515435548055088
2016 15.23359643366296