Annual % of total
1960 49.99384312276813
1961 45.59741160157152
1962 43.06852035749751
1963 39.6270606251689
1964 34.54746136865342
1965 30.973451327433633
1966 28.06876371616679
1967 25.629530000747213
1968 23.146747352496217
1969 19.3715661460584
1970 15.081192795984649
1971 10.063620589936379
1972 8.939440516446357
1973 15.31369879965351
1974 14.866844207723037
1975 19.433304845177833
1976 20.36709555460699
1977 22.216293134115972
1978 21.07757844843103
1979 25.87892898719441
1980 36.500030371135274
1981 34.95716207604617
1982 41.125452434610395
1983 39.823138200686984
1984 42.04037490987743
1985 46.6548650958369
1986 45.894291228288616
1987 47.1213073538655
1988 47.15863721054032
1989 42.04750450992183
1990 44.18284370199693
1991 50.331372549019605
1992 45.06402736362042
1993 46.65853938269523
1994 46.76745212850134
1995 39.711553738317754
1996 47.17572987721692
1997 38.41372410546139
1998 36.84187144291931
1999 31.24932935393258
2000 28.85040599506735
2001 29.662863509749304
2002 29.86315672471286
2003 36.23742500842602
2004 30.49822601595843
2005 28.244726477024066
2006 36.02744030235355
2007 32.86565917602996
2008 30.31932960893855
2009 31.70817916057632
2010 29.98750518887505
2011 28.474778370851705
2012 24.501049463491235
2013 28.60773636818409
2014 25.543895413870242
2015 19.49185119047619
2016 20.31464104013567