Annual % of total
1960 44.199071887423855
1961 44.15911346707507
1962 49.0496657421752
1963 51.626279505991334
1964 53.97489236859649
1965 56.08172970749894
1966 59.44922183786405
1967 60.624610711811265
1968 62.18319546684407
1969 64.16108790981964
1970 65.65402953079007
1971 54.56343091299915
1972 55.486535782587794
1973 56.67406100539895
1974 57.17408645015665
1975 58.71645531175159
1976 59.58846780602335
1977 61.20850972417567
1978 62.58027980521847
1979 62.989475572800785
1980 63.08263887059755
1981 63.04663535796166
1982 63.74684008695978
1983 63.83638517916163
1984 64.52158463127579
1985 65.0158356082925
1986 65.55925976970971
1987 66.35047916805213
1988 67.00423415223949
1989 67.34205324772815
1990 77.53389162179047
1991 77.22229160452332
1992 76.63729691990712
1993 76.60544280129791
1994 76.12479829528752
1995 76.61994623123744
1996 76.63946772412979
1997 76.65930979446634
1998 76.47603244824761
1999 76.61212864758909
2000 76.75693841277877
2001 77.00229411198289
2002 77.30281513606432
2003 78.1949768807328
2004 79.00807961983445
2005 79.59647315327322
2006 80.11736041672604
2007 80.53482363824536
2008 80.75770196870076
2009 80.86413943606117
2010 81.40758373041018
2011 81.87073808801506
2012 81.82094558670224
2013 81.59373065707643
2014 81.82835409497244
2015 88.9604814478969