Year % of total 1960 98.64864864864865 1961 98.70129870129871 1962 100 1963 100 1964 100 1965 100 1966 100 1967 100 1968 99.27536231884059 1969 100 1970 97.12643678160919 1971 90.9502262443439 1972 89.7872340425532 1973 89.38775510204083 1974 88.72180451127821 1975 89.58990536277602 1976 86.24161073825502 1977 88.52459016393442 1978 91.20879120879121 1979 86.57314629258516 1980 93.52112676056338 1981 95.12697323266988 1982 95.78034682080924 1983 95.32554257095158 1984 99.93946731234867 1985 99.94337485843715 1986 99.81617647058823 1987 99.80119284294236 1988 86.83333333333334 1989 95.96541786743515 1990 12.644827586206898 1991 -6.088603773584906 1992 97.6900395256917 1993 39.47806306306306 1994 36.31788751714678 1995 41.87909985935302 1996 54.71580441640379 1997 44.07077389984826 1998 41.9860650887574 1999 40.71944785276074 2000 44.606044776119404 2001 46.34439178515008 2002 47.45876205787781 2003 54.46396721311476 2004 52.650045871559634 2005 48.37555219364599 2006 48.38329496402878 2007 56.35980295566503 2008 52.74941534713764 2009 63.5780204778157 2010 63.2649276974416 2011 66.53051442910916 2012 69.13281869688386 2013 50.701126187245585 2014 68.3718064516129 2015 77.18554307116105 2016 69.82311111111112