Annual % of total
1960 93.4224049331963
1961 93.40054995417047
1962 93.87938793879388
1963 94.53874538745387
1964 95.26255707762557
1965 93.38609383832674
1966 93.6606291706387
1967 94.55017301038063
1968 94.01120206807411
1969 94.30331023864511
1970 94.32446007031642
1971 89.90765171503958
1972 88.90481064483113
1973 87.7931323283082
1974 80.53897978825793
1975 78.16330379030738
1976 78.75997544505833
1977 78.91663963671748
1978 82.67318920624902
1979 81.79862884796344
1980 82.31827111984283
1981 84.83226266952177
1982 82.907520690896
1983 80.4828585224529
1984 74.10695413231875
1985 76.50273224043715
1986 70.00183418928833
1987 68.89168765743072
1988 71.31576688696249
1989 64.89744909211204
1990 68.23008542445275
1991 66.68114953418602
1992 66.2157862639756
1993 76.28122348644473
1994 71.68746883116883
1995 73.89083690987124
1996 72.68483648521577
1997 69.10059024390243
1998 57.98728454968944
1999 47.27878644249687
2000 46.451681052198936
2001 50.87286345349846
2002 45.45756619966259
2003 44.15393366247131
2004 43.618833428589575
2005 41.89912745628268
2006 36.47675411165161
2007 37.024355952001706
2008 35.41381593993935
2009 36.10481769970169
2010 37.36247752498619
2011 35.99176773937621
2012 37.05964580873672
2013 39.46253844054226
2014 38.686470131215465
2015 33.13466824338852
2016 38.37808038838348