Annual % of total
1960 11.174267627321635
1961 11.836688446576273
1962 12.54867256637168
1963 10.602744484974814
1964 14.376474579407548
1965 15.096781699460465
1966 16.372300861179063
1967 15.998907302859225
1968 18.307238813182565
1969 18.98030514499755
1970 18.35402259353121
1971 19.149931882234267
1972 20.084281824566805
1973 21.470370619492837
1974 21.43381039249243
1975 21.650569703237245
1976 24.79452683777951
1977 25
1978 25.159589475911687
1979 25.48588587592179
1980 25.29887235151525
1981 25.60824812600735
1982 26.618635077793495
1983 27.924629878869446
1984 28.508284436632458
1985 29.692794217302914
1986 28.607899763713235
1987 27.638357561846465
1988 27.914961364349068
1989 29.903590425531913
1990 29.91467765794999
1991 30.730761872472335
1992 31.389003521126764
1993 33.57454812151036
1994 33.92990314935509
1995 34.19487697441602
1996 34.83159124276708
1997 33.96494284579859
1998 32.05121928671214
1999 32.90924021488872
2000 33.024361165048546
2001 32.47451335463763
2002 31.969970502597672
2003 33.483496956139064
2004 33.262710283852954
2005 33.60288724839537
2006 33.60529968395956
2007 31.708436225516795
2008 32.89169701926572
2009 34.48937423195084
2010 33.68995850699961
2011 34.898495946834146
2012 34.81016065358043
2013 35.69186968634852
2014 36.04080825160636
2015 35.781467788117396
2016 39.425179479726786