Annual % of total
1960 63.976816763263486
1961 63.00927793465107
1962 64.40677966101694
1963 63.49670811997075
1964 63.73918829008649
1965 65.25450521656654
1966 65.37747524752476
1967 69.76950354609929
1968 72.97068771138669
1969 74.32873274780427
1970 72.62677241047825
1971 78.25212337952615
1972 83.49320543565148
1973 81.02658111824013
1974 83.20056647194194
1975 84.27197802197801
1976 85.87080948487326
1977 85.04356243949663
1978 81.34472750725573
1979 83.03545268092589
1980 83.35371653757304
1981 84.32323232323232
1982 85.69816996741038
1983 84.65370595382747
1984 85.02397173858188
1985 79.76986887877977
1986 73.18274660579118
1987 68.68604651162791
1988 67.01191669450941
1989 69.53194518597616
1990 68.9917433649866
1991 68.29862520458265
1992 71.12113961941417
1993 67.94240663900415
1994 65.57185200845666
1995 67.62500690471494
1996 68.50985227739022
1997 68.53754761437267
1998 71.40097482014389
1999 65.13478540427585
2000 62.52217158611742
2001 65.7228201368524
2002 64.76634049687549
2003 63.54234798413747
2004 61.618348623853215
2005 60.648046433480985
2006 57.70747890818859
2007 58.13567006802721
2008 58.282332864180155
2009 55.26553285968028
2010 57.45254613270514
2011 53.12627832364147
2012 49.430734135213605
2013 52.146063144329894
2014 52.88527759634226
2015 49.70495285857573
2016 53.33544708777686