Annual % of total
1960 57.179161372299866
1961 54.72109691492677
1962 50.17991494929669
1963 49.26536731634184
1964 48.40514829322887
1965 42.66595289079229
1966 41.60125588697017
1967 38.03763440860216
1968 35.91625883632409
1969 35.5601233299075
1970 35.081374321880645
1971 30.168005843681517
1972 28.797826579126106
1973 29.29089443996777
1974 29.794721407624632
1975 28.775100401606423
1976 27.983225314525356
1977 25.704479768786126
1978 24.231317450621052
1979 22.857778766970846
1980 22.978365889519008
1981 24.118038606611936
1982 21.994370727784478
1983 24.045723617064706
1984 22.044849866970733
1985 18.41574167507568
1986 15.24907896844466
1987 17.186311787072242
1988 19.491770141495813
1989 16.469399538106234
1990 20.479973106230393
1991 18.278235294117646
1992 15.110024600246003
1993 21.716737766624842
1994 18.954221581548598
1995 18.304917965545528
1996 14.322870588235293
1997 16.33146297627606
1998 16.12192392099488
1999 16.949177986764195
2000 15.028484745762713
2001 17.190507566204285
2002 14.15475934135529
2003 20.670738636363637
2004 25.056531791907517
2005 24.864100992410975
2006 22.273471291168757
2007 19.636406109613656
2008 21.99986616235089
2009 18.615996168582374
2010 16.679961451975586
2011 18.715594728171332
2012 20.11637613245861
2013 17.844141732283468
2014 17.325681031770994
2015 16.711677539608573
2016 14.536279666452856