Annual % of total
1960 28.756130182790905
1961 30.17345703912868
1962 28.064643279463937
1963 29.370885149963428
1964 28.942115768463072
1965 27.537148276952262
1966 27.382425742574256
1967 22.901891252955085
1968 19.898534385569334
1969 18.695106649937262
1970 19.730833934150443
1971 14.282521233795265
1972 8.952837729816146
1973 10.74243813015582
1974 8.620994866348026
1975 7.675137362637361
1976 5.870809484873262
1977 5.517909002904163
1978 7.4330861012576595
1979 6.724289481394667
1980 6.033428454953118
1981 5.239057239057239
1982 4.136375031336174
1983 5.321992709599028
1984 5.475649760282614
1985 10.462938185710463
1986 17.926228523368977
1987 22.05813953488372
1988 24.056130972268626
1989 23.224773091297386
1990 25.2145312880448
1991 25.84990647650222
1992 23.96839640795382
1993 26.251203319502075
1994 26.785380549682873
1995 26.70855000986388
1996 26.62600123102175
1997 26.078684468878855
1998 21.19737050359712
1999 23.130217006912073
2000 23.29490593577684
2001 19.85246171391333
2002 20.09276787075141
2003 20.57082782551223
2004 20.74012232415902
2005 19.508417595845426
2006 20.576449958643504
2007 18.60940136054422
2008 17.08342012667136
2009 19.097058614564833
2010 12.374505300353357
2011 16.80187487467415
2012 23.087955205309
2013 21.58772981099656
2014 22.131338994121492
2015 24.78994984954865
2016 22.140377358490564