Annual % of total
1960 33.177387914230025
1961 33.445315416200074
1962 32.467532467532465
1963 35.686509123541725
1964 37.35440931780366
1965 37.47576997630842
1966 33.837986629964604
1967 32.34465928289844
1968 29.83407261376705
1969 31.409241399165104
1970 23.61153262518968
1971 24.073829927488465
1972 22.07897793263647
1973 22.81496062992126
1974 24.84560089095879
1975 29.233091217809644
1976 31.259613741240816
1977 29.36724662557541
1978 24.82458816351434
1979 26.429796968830427
1980 24.96969696969697
1981 28.16657027183343
1982 29.850221503410452
1983 34.5348913976365
1984 36.14628189472331
1985 39.21699140747913
1986 41.20930232558139
1987 41.83372811831995
1988 42.829405102205925
1989 42.372713791398915
1990 41.975075376884426
1991 40.32152334476392
1992 41.04619723714505
1993 41.17802919708029
1994 41.82118525021949
1995 39.84830275229358
1996 37.74670492991783
1997 40.181143744030564
1998 40.31469413520028
1999 38.57482608695652
2000 37.67545521914038
2001 37.930163544146566
2002 36.64722360248447
2003 35.05274396328078
2004 35.9391707561342
2005 34.62338597351643
2006 33.0612641509434
2007 33.44630236794172
2008 32.66372672044617
2009 35.144986278235166
2010 35.40970427038136
2011 36.82613483146067
2012 40.10852790610563
2013 38.030958885209714
2014 37.97757153127247
2015 32.53983972945155
2016 25.786936424831712